PubMed · 7366718
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Y Edwards, D A Hopkinson. 1980-04-10. Are abundant proteins less variable?. https://doi.org/10.1038/284511a0
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Inactivation of Saccharomyces cerevisiae poly(A) polymerase in a strain bearing the temperature-sensitive lethal pap1-1 mutation results in the synthesis of poly(A)- mRNAs that initiate translation with surprising efficiency. Translation of poly(A)- mRNAs after polyadenylation shut-off might result from an increase in the ratio of ribosomes and associated translation factors to mRNA, caused by the inability of poly(A)- mRNAs to accumulate to normal levels. To test this hypothesis, we used ribosomal subunit protein gene mutations to decrease either 40 or 60 S ribosomal subunit concentrations in strains carrying the pap1-1 mutation. Polyadenylation shut-off in such cells results in a nearly normal ratio of ribosomes to mRNA as revealed by polyribosome sedimentation analysis. Ribonuclease protection and Northern blot analyses showed that a significant percentage of poly(A)-deficient and poly(A)- mRNA associate with smaller polyribosomes compared with cells with normal ribosome levels. Analysis of the ratio of poly(A)-deficient and poly(A)- forms of a specific mRNA showed relatively more poly(A)- mRNA sedimenting with 20-60 S complexes than do poly(A)+ forms, suggesting a block in an early step of the translation initiation of the poly(A)- transcripts. These findings support models featuring the poly(A) tail as an enhancer of translation and suggest that the full effect of a poly(A) tail on the initiation strength of a mRNA may require competition for a limited number of free ribosomes or translation factors.
The dopamine D4 receptor gene (DRD4) and its products are of great interest in many neurospsychiatric disorders. There are at least five expressed polymorphisms in exons 1 and 3, plus rare expressed variants, all of which may have functional relevance. Several studies have described methods for studying the exon 3 polymorphisms, especially the VNTR; fewer reports have documented the exon 1 polymorphisms and variants of DRD4. We report here a simple, rapid, nonisotopic, nondenaturing heteroduplex method for determining the molecular haplotype composed of the two more polymorphic systems of the first exon of DRD4: the 12 bp duplication and 13 bp deletion. This method will facilitate future research on expressed variation of this gene.