July 1999
Volume 40, Issue 8
Free
Biochemistry and Molecular Biology  |   July 1999
Screening of the Gene Encoding the α′-Subunit of Cone cGMP-PDE in Patients with Retinal Degenerations
Author Affiliations
  • Yong Qing Gao
    From the Jules Stein Eye Institute, University of California Los Angeles School of Medicine;
  • Michael Danciger
    From the Jules Stein Eye Institute, University of California Los Angeles School of Medicine;
    Loyola Marymount University, Los Angeles, California; the
  • Reid Longmuir
    Department of Ophthalmology, University of Iowa, Iowa City; the
  • Natik I. Piriev
    From the Jules Stein Eye Institute, University of California Los Angeles School of Medicine;
  • Dan Yun Zhao
    From the Jules Stein Eye Institute, University of California Los Angeles School of Medicine;
  • John R. Heckenlively
    From the Jules Stein Eye Institute, University of California Los Angeles School of Medicine;
  • Gerald A. Fishman
    University of Illinois at Chicago; the
  • Richard G. Weleber
    Casey Eye Institute, Oregon Health Sciences University, Portland; the
  • Samuel G. Jacobson
    Scheie Eye Institute, University of Pennsylvania, Philadelphia; and the
  • Edwin M. Stone
    Department of Ophthalmology, University of Iowa, Iowa City; the
  • Debora B. Farber
    From the Jules Stein Eye Institute, University of California Los Angeles School of Medicine;
    Molecular Biology Institute, University of California Los Angeles.
Investigative Ophthalmology & Visual Science July 1999, Vol.40, 1818-1822. doi:
  • Views
  • PDF
  • Share
  • Tools
    • Alerts
      ×
      This feature is available to authenticated users only.
      Sign In or Create an Account ×
    • Get Citation

      Yong Qing Gao, Michael Danciger, Reid Longmuir, Natik I. Piriev, Dan Yun Zhao, John R. Heckenlively, Gerald A. Fishman, Richard G. Weleber, Samuel G. Jacobson, Edwin M. Stone, Debora B. Farber; Screening of the Gene Encoding the α′-Subunit of Cone cGMP-PDE in Patients with Retinal Degenerations. Invest. Ophthalmol. Vis. Sci. 1999;40(8):1818-1822.

      Download citation file:


      © ARVO (1962-2015); The Authors (2016-present)

      ×
  • Supplements
Abstract

purpose. To screen the exons of the gene encoding the α′-subunit of cone cyclic guanosine monophosphate (cGMP)-phosphodiesterase (PDE6C) for mutations in a group of 456 unrelated patients with various forms of inherited retinal disease, including cone dystrophy, cone–rod dystrophy, macular dystrophy, and simplex/multiplex and autosomal recessive retinitis pigmentosa.

methods. The 22 exons of the PDE6C gene were screened for mutations either by denaturing gradient gel electrophoresis and single-strand conformation polymorphism electrophoresis (SSCP) or by SSCP alone; variants were sequenced directly.

results. Although many sequence variants were found, none could be associated with disease.

conclusions. The results show that PDE6C was not the site of the mutations responsible for the types of inherited retinal degenerations analyzed in the large population of patients in the present study. The types of degeneration included those that predominantly affect cone-mediated function (cone and cone–rod dystrophies) or rod-mediated function (retinitis pigmentosa) or that have a predilection for disease in the macula (macular dystrophies).

In mammalian rods the visual response is induced by a cascade of events mediated by rhodopsin, rod transducin, and rod cyclic guanosine monophosphate-phosphodiesterase (cGMP-PDE). Activated rod cGMP-PDE breaks down cGMP causing the cGMP-gated cation channels to close, bringing about an eventual alteration in the flow of neurotransmitter from the rod synaptic terminal. 1 The same basic cascade most likely occurs in the cone visual cell. However, the proteins making up the cascade are different. For example, instead of rhodopsin, one of the cone opsins is present, and instead of one α- and one β- catalytic subunit in rod cGMP-PDE, there are two identical catalytic α′-subunits in cone cGMP-PDE. 
Retinal degenerations such as retinitis pigmentosa (RP) have been associated with mutations in several genes including those for both theα - and β-subunits of rod cGMP-PDE (PDE6A and PDE6B). 2 3 4 5 Mutations in these genes are associated with autosomal recessive (AR) RP, and they were detected by exon screening of large numbers of unrelated patients. Therefore, the gene for the α′-subunit of cone cGMP-PDE (PDE6C) was a good candidate for screening in autosomal recessive and simplex diseases involving cones such as cone and cone-rod dystrophy. Considering that mutations in a gene expressed in rods are responsible for diseases that significantly affect cones, 6 7 it seemed reasonable to analyze a spectrum of retinal degenerative diseases including RP and macular dystrophies for cone cGMP-PDE-α′ mutations as well. 
In this study, we have screened patients’ DNAs for mutations in the 22 exons of the cGMP-PDE α′ gene (PDE6C). The PDE6C exons of one subgroup of 91 patients were screened both by single-strand conformation polymorphism electrophoresis (SSCP) and denaturing gradient gel electrophoresis (DGGE), whereas exons of the remaining subgroup of 365 patients were screened only by SSCP. 
Methods
Subjects
Four hundred fifty-six unrelated patients with retinal degenerative disease were included in this study. Exons in which potential mutant sequence variants were present were screened in control subjects: either in one set of 96 subjects or in a separate set of 30 to 68 subjects. Control subjects self-reported normal vision; their ages and ethnicities were not determined, nor were they examined ophthalmologically. All participants were fully informed of the nature of the investigations, and the research was performed in accordance with institutional guidelines and the Declaration of Helsinki. 
All patients were examined clinically with best corrected visual acuity, intraocular pressure, biomicroscopy, direct and indirect ophthalmoscopy, and fundus photography. Visual function testing included standardized Goldmann visual fields and electroretinography. Patients were then categorized into three groups by the mode of inheritance and clinical diagnosis: those with retinal degenerations that have significant effects on cone-mediated function throughout the retina (cone dystrophy and cone–rod dystrophy [CRD]), those with a predilection for disease in the macula versus the peripheral retina (macular dystrophies and Stargardt disease/fundus flavimaculatus), 8 and those with simplex/multiplex or autosomal recessive RP (Table 1) . Patients with age-related macular degeneration were not included, nor were any patients in whom toxic retinopathy was suspected. 
Screening of Exons by SSCP and DGGE
DNAs were extracted from blood samples by standard methods and were screened for sequence variants in the PDE6C gene in two laboratories (DBF, EMS). In DBF’s laboratory, exons were screened by both SSCP and DGGE. For SSCP, exons were amplified by polymerase chain reaction (PCR) directly from genomic DNAs with primer pairs that flanked each exon and included intronic sequence on each side. The sequences of the primer pairs are shown in Table 2 . The primer pairs were derived from the gene sequences in the GenBank database on the World Wide Web that were deposited by Piriev et al. 9 (GenBank Database www2.ncbi.nlm.nih.gov/ GenBank Accession numbers U20196 and U20212) The PCR and SSCP protocols have been previously described. 4  
For DGGE, fragments were amplified directly from genomic DNAs by the same primer pairs used for SSCP, except that one primer of each pair (usually the one with the greater GC content) had a 36-bp “GC clamp” (see Table 2 ) included before the first 5′ base of the primer; its sequence was kindly provided by John Nakamoto and Neil van Dop (Department of Endocrinology, University of California Los Angeles). The PCR and DGGE protocols have been previously described. 4  
In EMS’s laboratory, exons were screened by SSCP alone. The PCR protocol was as follows: 5 minutes at 94°C followed by 35 cycles of[ 94° for 30 seconds; 50°, 55°, 60°, or 63° for 30 seconds; and 72° for 30 seconds]. Amplified PCR products were denatured with NaOH, formamide, and heat before they were electrophoresed in sequence-sized 6% nondenaturing acrylamide gels with 5% glycerol. Gels were run at 25 W for approximately 3 hours. After electrophoresis, gels were stained with silver nitrate. 10  
Direct Sequencing
The same primers used to amplify exons by SSCP were used to produce fragments for sequencing. The amplicons were purified and sequenced directly by the standard dideoxy method using[γ -32P]adenosine triphosphate as label and a sequencing kit (fmol; Promega, Madison, WI). In some cases, amplicons were first subcloned into PCR-script (Stratagene, San Diego, CA) before they were sequenced with M13 and reverse M13 primers (these primers match vector sequences that flank inserts). In some other cases, PCR products were sequenced using fluorescent dideoxynucleotides on an automated sequencer (model 373; Applied Biosystems, Foster City, CA). All heterozygous base changes were recognized by the approximately equal peak intensity of two fluorescent dyes at the variant base. All sequencing, regardless of method, was performed bidirectionally. 
Results
Exon Screening
Sequence variants were not found in the amplicons of exons 2, 3, 4, 5, 6, 7, 9, 11, 12, 13, 14, 18, and 19 of the PDE6C gene in any of the 456 patients. In the subset of 91 patients screened by both DGGE and SSCP (in DBF’s laboratory), several variants were found (Table 3) . A heterozygous T–G transversion creating Asp157Glu was detected in 1 patient with AR cone–rod dystrophy (CRD) and 1 of 42 control subjects tested. A second mutation was not found in this patient. A G–A transition in exon 8 creating AL366AL was found in many patients and control subjects. There were two transitions in intron 9: One was a G–A at the seventh base pair upstream of exon 10 (IVS9−7G→A), and the other was a C–T at the ninth base pair (IVS9−9C→T). Both were common polymorphisms in patients and control subjects, as were two other base changes: a C–A transversion 10 bp downstream of exon 15 (IVS15+10C→A) and an A–G transition 71 bp upstream of exon 20 (IVS19−71A→G). 
There were three additional variants: 1) an A–G transition in the ninth base pair upstream of exon 16 (IVS15−9A→G), 2) a T–C transition in the 29th base pair downstream of exon 17 (IVS17+29T→C); and 3) a G–C transversion in exon 21 creating Lys822Asn. The first was present in 2 patients with AR–CRD and in 0 of 50 control subjects. However, second significant mutations were not found in either of the two patients, and based on the scoring system of Shapiro and Senapathy, 11 this A–G change does not alter the score (efficacy) of this 3′ intronic 14-bp splice site. The second variant was found in two patients with AR-CRD and two with simplex CRD and in 0 of 68 control subjects. Second significant mutations were not found in any of the four patients, and because splice branch points are approximately 30 to 50 bp upstream of the exon, 12 this downstream variant could not alter an existing branch point or create a new one. The third variant was present in one simplex CRD patient and in 0 of 40 control subjects. However, no second significant mutation was found in the patient, neither parent had disease, and the mother carried the same variant. 
In the set of 365 patients whose DNAs were screened only by SSCP (in EMS’s laboratory), sequence variants were found in amplicons of exons 8, 10, 20, 21, and 22 (Table 3) . The variant in the exon 8 amplicon was the same AL366AL detected in DBF’s laboratory, as was IVS9−9C→T; both were also found to be common in patients and control subjects tested in EMS’s laboratory. A 6-bp deletion in a stretch of 22 A’s starting 96 bp upstream of exon 20 (IVS19–96 to IVS19–75) was found in only 1 patient and 0 of 96 control subjects, but this deletion did not alter or create a branch point (PyNPyPuAPy 12 ) or create a splice site. 11 It was essentially an unchanged sequence. 
Three patients and 0 of 96 control subjects had an A–G transition in exon 21 creating Glu834Gly. However in the family of one of the patients, an affected sibling did not carry the variant. The last variant was a 3-bp insertion between the sixth and seventh base pairs after the TAA stop signal in exon 22. This insert was also absent from an affected sibling. 
Discussion
In our screening for exonic mutations in PDE6C in 456 unselected patients with several different forms of retinal disease, we found a number of sequence variants. Five were common polymorphisms present in equal numbers in patients and control subjects, whereas seven others were rare heterozygous sequence variants (Table 3)
The variants were three rare amino acid changes: Asp157Glu, Lys 822Asn, and Glu834Gly. None of them could be associated with disease because of the absence of a second variant in autosomal recessive disease, and/or the absence of cosegregation of variant with disease in the probands’ families. The Lys822Asn variant was interesting, because this lysine residue is in the catalytic site of the α′-subunit and is conserved in bovine and chick cone cGMP-PDE α′-subunits and in human, dog, mouse, and bovine rod cGMP-PDE α-subunits. However, there was no evidence for autosomal recessive disease, because no second variant was found in the patient, and autosomal dominant disease was ruled out because the mother carried the variant without disease. Moreover, the amino acid change was conservative. In addition to not cosegregating with disease in one of the proband’s families, the Glu834Gly variant was also not significant, because this amino acid residue is in the C-terminal portion of the protein between the highly conserved catalytic site and the highly conserved isoprenylation site in an area with no known functional significance. 
There were four additional heterozygous rare sequence variants (Table 3) that were not present in control subjects. None of these could be associated with disease, because second variants could not be found in autosomal recessive cases, and/or they did not cosegregate with disease in the probands’ families, and/or they did not create new or influence existing branch points, and/or they did not influence the sequences around them to create new or influence existing splice sites. 
It should be noted that PDE6C (or any gene for which negative exon screening results have been obtained) cannot be definitively ruled out as the site for mutations responsible for disease. This is because the SSCP or DGGE techniques may not detect all sequence variants (although only a very small percentage of mutations may remain undetected), mutations may be present in 5′, 3′, or intronic sequences not screened, mutations in this gene may be so rare that not enough patients were screened to detect them, and mutations in this gene may be present only in specific diseases not screened. 
Nevertheless, in the patients analyzed, we could find no sequence variants in the gene encoding the α′-subunit of cone cGMP-PDE that could be associated with simplex or autosomal recessive retinal degenerations that predominantly affect cone-mediated function and rod-mediated function or that have a predilection for disease in the macula. 
 
Table 1.
 
Table 1.
 
Diagnoses of Patients Screened for Mutations in PDE6C
Table 1.
 
Table 1.
 
Diagnoses of Patients Screened for Mutations in PDE6C
Group 1
Cone-rod dystrophy
Autosomal recessive 28
Simplex 158
Cone dystrophy
Simplex 11
197
Group 2
Macular dystrophies
Simplex 130
Stargardt/fundus flavimaculatus
Recessive 5
Simplex 20
155
Group 3
Retinitis pigmentosa
Simplex/multiplex and recessive 104
Total 456
Table 2.
 
Table 2.
 
Primer Pairs Used to Amplify the Exons of the Genes Encoding theα′ -Subunit of Cone cGMP-phosphodiesterase
Table 2.
 
Table 2.
 
Primer Pairs Used to Amplify the Exons of the Genes Encoding theα′ -Subunit of Cone cGMP-phosphodiesterase
Exon Primer Pair Exon Primer Pair
1a GTGCTCTGAAGGTCGTCCTT * AGCAGGTGGGCCAGCCTCTG 11 * TAGTAGAGGAATCAGATGGAAATC ATTTAACAGGCATTAAGGTTAGAA
1b * GTGGACCGTGCAGGAGGAGG CCACTGTCATAAGGCCACCT 12 AACAACCCATCCTTATTTCAA * GTGAAGCAGAGCCACAGAATC
2 GTGGACCGTGCAGGAGGAGG * CCACTGTCATAAGGCCACC 13 * TCTGAATGGGTCATCTTCTT CTATTTCTCATCATGCTCAA
3 GATGTCACAACCATAACTTGT * GCATGGTAAGACTAATGCTGC 14 * AGGCTCCACGTGGTATAGA ACGTGTCAACATTGGACATG
4 TCTATCTCTCCATAGCATA * TAGGCGATGTGAGATGAGACA 15 * AGCTAGAATCATGGCATGTTG TGTGCTGTCCTAAAGAGA
5 * AAGATATGGTAGGTCATGGAACAG AGATGGCATCAAGGAAGACATTTG 16 CAAATTATTGATAGCATTTTATTC * ACACAGACTATAGGGCATTCCACT
6 AATAACATTATTCCCATAATA * AACGGCAACTGCGGCAGCAAC 17/18 CTTTTCATAAGCTAAAATTGTTGC * GTACCTGACAGTGTGTGACA
7 * GACTTTCTCTATATTGCAATGA AATTTGAATTGTTCAATAAC 19 GTGGATTTAGTGAACCAAGCC * ATTACAGGTGTGAGGCCACCG
8 CTCCACTACACAATATTTCAGACC * CAGCCCCAAGAGGTGAGGTCTGAC 20 AGACAGAGTGAGACTCTGCCT * TGGCTTTCCGTATGGGTGTCT
9 * AACTTGAGGTCCCTTCTCGTT CATTGACTTCCATTATCTTAT 21 TAACTGTATGATTTATGTAGT * CCTAGCTTCTGGCTACATTAC
10 TCACTGAAGAGAATTAGAA * CTTATGTCCACAGGACTGAA 22 * CCACTAACTCCTAATAATATTGCT AGGTAAAATGATATTTGAAGT
Table 3.
 
Table 3.
 
Sequence Variants Found in the Exons of the PDE6C Gene in the DNAs of 456 Patients with Retinal Degenerations
Table 3.
 
Table 3.
 
Sequence Variants Found in the Exons of the PDE6C Gene in the DNAs of 456 Patients with Retinal Degenerations
Sequence Variant Exon Number of Patients with Variant Number of Patients Tested Number of Control Subjects with Variant/Total
Ala366Ala 8 Common 456 Common
IVS9−9C→T Common 456 Common
IVS9−7G→A Common 91 Common
IVS14+10C→A Common 91 Common
IVS19−71A→G Common 91 Common
Asp157Glu 1 1 91 1/42
Lys822Asn 21 1 91 0/40
Glu834Gly 21 3 365 0/96
IVS15−9A→G 2 91 0/50
IVS17+29T→C 4 91 0/68
Deletion of 6 of 22 consecutive As (IVS19–96 to IVS19–75) 1 365 0/96
Insertion of 3 bp between the Sixth and Seventh Base Pairs Downstream of the Stop Codon 22 1 365 0/96
Farber DB, Danciger M. Identification of genes causing photoreceptor degenerations leading to blindness. Curr Opin Neurobiol. 1997;7:666–673. [CrossRef] [PubMed]
Huang SH, Pittler SJ, Huang X, Oliveira L, Berson EL, Dryja TP. Autosomal recessive retinitis pigmentosa caused by mutations in the alpha subunit of rod cGMP phosphodiesterase. Nat Genet. 1995;11:468–471. [CrossRef] [PubMed]
McLaughlin ME, Ehrhart TL, Berson EL, Dryja TP. Mutation spectrum of the gene encoding the beta subunit of rodphosphodiesterase among patients with autosomal recessive retinitis pigmentosa. Proc Natl Acad Sci USA. 1995;92:3249–3253. [CrossRef] [PubMed]
Danciger M, Blaney J, Gao YQ, et al. Mutations in the PDE6B gene in autosomal recessive retinitis pigmentosa. Genomics. 1995;30:1–7. [CrossRef] [PubMed]
Bayes M, Giordano M, Balcells S, et al. Homozygous tandem duplication within the gene encoding the beta-subunit of rod phosphodiesterase as a cause for autosomal recessive retinitis pigmentosa. Hum Mutat. 1995;5:228–234. [CrossRef] [PubMed]
Cremers FP, van de Pol DJ, van Driel M, et al. Autosomal recessive retinitis pigmentosa and cone-rod dystrophy caused by splice site mutations in the Stargardt’s disease gene ABCR. Hum Mol Genet. 1998;7:355–362. [CrossRef] [PubMed]
Allikmets R, Singh N, Sun H, et al. A photoreceptor cell-specific ATP-binding transporter gene (ABCR) is mutated in recessive Stargardt macular dystrophy. Nat Genet. 1997;15:236–246. [CrossRef] [PubMed]
Weleber RG, Eisner A. Cone degeneration and color vision defects. Newsome DA eds. Retinal Dystrophies and Degenerations. 1988;233–256. Raven Press New York.
Piriev NI, Viczian AS, Ye J, Kerner B, Korenberg JR, Farber DB. Gene structure and amino acid sequence of the human cone photoreceptor cGMP-phosphodiesterase alpha′ subunit (PDEA2) and its chromosomal localization to 10q24. Genomics. 1995;28:429–435. [CrossRef] [PubMed]
Bassam BJ, Caetano–Anolles G, Gresshoff PM. Fast and sensitive silver staining of DNA in polyacrylamide gels. Anal Biochem. 1991;196:80–83. [CrossRef] [PubMed]
Shapiro MB, Senapathy P. RNA splice junctions of different classes of eukaryotes: sequence statistics and functional implications in gene expression. Nucleic Acids Res. 1987;15:7155–7174. [CrossRef] [PubMed]
Sharp PA. Splicing of messenger RNA precursors. Science. 1987;235:766–771. [CrossRef] [PubMed]
Table 1.
 
Table 1.
 
Diagnoses of Patients Screened for Mutations in PDE6C
Table 1.
 
Table 1.
 
Diagnoses of Patients Screened for Mutations in PDE6C
Group 1
Cone-rod dystrophy
Autosomal recessive 28
Simplex 158
Cone dystrophy
Simplex 11
197
Group 2
Macular dystrophies
Simplex 130
Stargardt/fundus flavimaculatus
Recessive 5
Simplex 20
155
Group 3
Retinitis pigmentosa
Simplex/multiplex and recessive 104
Total 456
Table 2.
 
Table 2.
 
Primer Pairs Used to Amplify the Exons of the Genes Encoding theα′ -Subunit of Cone cGMP-phosphodiesterase
Table 2.
 
Table 2.
 
Primer Pairs Used to Amplify the Exons of the Genes Encoding theα′ -Subunit of Cone cGMP-phosphodiesterase
Exon Primer Pair Exon Primer Pair
1a GTGCTCTGAAGGTCGTCCTT * AGCAGGTGGGCCAGCCTCTG 11 * TAGTAGAGGAATCAGATGGAAATC ATTTAACAGGCATTAAGGTTAGAA
1b * GTGGACCGTGCAGGAGGAGG CCACTGTCATAAGGCCACCT 12 AACAACCCATCCTTATTTCAA * GTGAAGCAGAGCCACAGAATC
2 GTGGACCGTGCAGGAGGAGG * CCACTGTCATAAGGCCACC 13 * TCTGAATGGGTCATCTTCTT CTATTTCTCATCATGCTCAA
3 GATGTCACAACCATAACTTGT * GCATGGTAAGACTAATGCTGC 14 * AGGCTCCACGTGGTATAGA ACGTGTCAACATTGGACATG
4 TCTATCTCTCCATAGCATA * TAGGCGATGTGAGATGAGACA 15 * AGCTAGAATCATGGCATGTTG TGTGCTGTCCTAAAGAGA
5 * AAGATATGGTAGGTCATGGAACAG AGATGGCATCAAGGAAGACATTTG 16 CAAATTATTGATAGCATTTTATTC * ACACAGACTATAGGGCATTCCACT
6 AATAACATTATTCCCATAATA * AACGGCAACTGCGGCAGCAAC 17/18 CTTTTCATAAGCTAAAATTGTTGC * GTACCTGACAGTGTGTGACA
7 * GACTTTCTCTATATTGCAATGA AATTTGAATTGTTCAATAAC 19 GTGGATTTAGTGAACCAAGCC * ATTACAGGTGTGAGGCCACCG
8 CTCCACTACACAATATTTCAGACC * CAGCCCCAAGAGGTGAGGTCTGAC 20 AGACAGAGTGAGACTCTGCCT * TGGCTTTCCGTATGGGTGTCT
9 * AACTTGAGGTCCCTTCTCGTT CATTGACTTCCATTATCTTAT 21 TAACTGTATGATTTATGTAGT * CCTAGCTTCTGGCTACATTAC
10 TCACTGAAGAGAATTAGAA * CTTATGTCCACAGGACTGAA 22 * CCACTAACTCCTAATAATATTGCT AGGTAAAATGATATTTGAAGT
Table 3.
 
Table 3.
 
Sequence Variants Found in the Exons of the PDE6C Gene in the DNAs of 456 Patients with Retinal Degenerations
Table 3.
 
Table 3.
 
Sequence Variants Found in the Exons of the PDE6C Gene in the DNAs of 456 Patients with Retinal Degenerations
Sequence Variant Exon Number of Patients with Variant Number of Patients Tested Number of Control Subjects with Variant/Total
Ala366Ala 8 Common 456 Common
IVS9−9C→T Common 456 Common
IVS9−7G→A Common 91 Common
IVS14+10C→A Common 91 Common
IVS19−71A→G Common 91 Common
Asp157Glu 1 1 91 1/42
Lys822Asn 21 1 91 0/40
Glu834Gly 21 3 365 0/96
IVS15−9A→G 2 91 0/50
IVS17+29T→C 4 91 0/68
Deletion of 6 of 22 consecutive As (IVS19–96 to IVS19–75) 1 365 0/96
Insertion of 3 bp between the Sixth and Seventh Base Pairs Downstream of the Stop Codon 22 1 365 0/96
×
×

This PDF is available to Subscribers Only

Sign in or purchase a subscription to access this content. ×

You must be signed into an individual account to use this feature.

×