The suggestion that compensation for overabundant mRNA of the genes for Saccharomyces cerevisiae ribosomal protein (r-protein) L3, L29, or rp59 occurs by translation repression has been reinvestigated. First, analysis of the distribution of these three mRNAs in polysome profiles revealed no differences between normal and mRNA-overproducing strains, indicating that initiation of r-protein translation is not repressed under conditions of mRNA overaccumulation. Second, experiments involving radioactive pulse-labeling of proteins were done by using a modified method of data collection and analysis that allows quantitation and correction for fast decay during the pulse. These measurements revealed that the synthesis rate of the three r-proteins is increased when their mRNA levels are elevated and that their decay rate is also high, with half-lives ranging from a fraction of a minute to more than 10 min. We conclude that accumulation of excess r-protein mRNA has no effect on translation rate; rapid decay of protein during the course of the labeling period can account for the apparent discrepancy between mRNA levels and protein synthesis rates. Yeast r-proteins, when produced in excess, are among the most rapidly degraded proteins so far described.

Saccharomyces cerevisiae mRNA 5'-ends map at a variable distance from the TATA element. The mechanism for the choice of the transcription Initiation Region (IR) over other neighbouring sequences is not clearly understood. Sequences on the coding strand flanking the IR of 95 yeast RNA polymerase II promoters have been compared. They indicate the following pattern: statistically, a preponderance of T residues beginning as far as 30 nucleotides upstream and ending approximately 10 nucleotides upstream of the IR, and a preponderance of A residues from approximately 8 nucleotides upstream of the transcription initiation-site onward. The switch in base composition noted above thus occurs over a short region that is centered typically -9 nucleotides with respect to the major transcription start-site. We call this overall sequence pattern the locator. It is more evident among strong promoters than weak ones, suggesting a role in transcription initiation. The promoter of the TCM1 gene (coding for ribosomal protein L3) has a typical locator in the region of its IR. In an attempt to confirm the role of this sequence motif in defining the IR, deletions were introduced between the TATA element and the IR of the TCM1 gene. In most deletions, the new transcription start-sites are found within a recognizable locator, supporting the suggestion that this sequence pattern is important in defining the IR. These data appear to indicate that in yeast the IR is defined by a pattern of base composition situated at a suitable distance from the TATA element.

In the present study, we examined the expression of the mammaglobin genes, MGB1 and MGB2, in the sentinel lymph nodes (SLNs) of patients with breast cancer and compared our results with the histologic status of the same SLNs. Compared with immunohistochemical staining for cytokeratin 8, which detected metastases in 17 of 42 patients, reverse transcription-polymerase chain reaction (RT-PCR) for MGB1 or MGB2 genes was positive in 22 patients. The concordance between the expression of any mammaglobin and histologic status was 79% (33/42), with a sensitivity of 88% and specificity of 72%. The detection of patients with metastases was more sensitive when testing for both MGB1 and MGB2 (P< .0001) rather than MGB2 (P < .0005) or MGB1 (P < .05) alone. The increased detection rate relative to histologic examination suggests that using RT-PCR for the mammaglobin genes might identify patients at higher risk compared with patients with negative RT-PCR results.