Translational efficiencies of polyomavirus late mRNA molecules that differ in the sequences of their 5' noncoding late leader exons

Effects of long 5' leader sequences on initiation by eukaryotic ribosomes in vitro

Lengthening the 5' noncoding sequence on SP6-derived transcripts can increase their translational efficiency by an order of magnitude under some conditions of translation in reticulocyte lysates. This effect was observed upon reiterating three different synthetic oligonucleotides, the sequences of which were designed simply to preclude secondary structure. It seems unlikely that such arbitrarily designed sequences are recognized by sequence-specific translational enhancer proteins. Rather, long 5' leader sequences appear to accumulate extra 40S ribosomal subunits, which may account for their translational advantage. The buildup of 40S subunits on long, unstructured leader sequences is predicted by the scanning model for initiation. Leader sequences such as these may be ideal for in vitro expression vectors.

RNA processing in the polyoma virus life cycle

Not only is gene regulation in polyoma interesting, but it has also proven to be highly informative and illustrative of a number of novel concepts in gene regulation. Of special interest and importance are the mechanisms by which this virus switches from the expression of early gene products to late gene products after the onset of viral DNA replication. This switch is mediated at least in part by changes in transcription elongation and polyadenylation in the late region, and by the formation and editing of dsRNA in the nucleus. In this review we will summarize the regulation of RNA synthesis and processing during polyoma infection, and will point out in particular those aspects that have been most novel.