Utilization of Messenger in Adenovirus-2-infected Cells at Normal and Elevated Temperatures

THE regulation of protein synthesis in eukaryotic cells appears to be distinctly different from that in prokaryotes. The long-lived messenger RNA in eukaryotes suggests that control of protein synthesis occurs partially at the level of translation and regulation at the level of initiation of translation of messenger RNA has been found under several different conditions in mammalian cells^1–6.     

Selective Interruption of High Molecular Weight RNA Synthesis in HeLa Cells by Camptothecin

THE study of macromolecular metabolism in eukaryotic cells has depended to a large extent on the use of selective inhibitors. Camptothecin is a potent, rapidly acting inhibitor of both DNA and RNA synthesis^1–3 which first came to attention as a potential anti-tumour agent⁴ and which has since been shown to have the remarkable property of inducing breaks in cellular DNA⁵; it also has unusual effects on RNA synthesis possibly as a result of DNA breakage. We show that the drug causes aberrant synthesis of high molecular weight nuclear RNA, but has a much smaller effect on the labelling of 4S RNA and does not affect 5S RNA synthesis. If the effect on RNA synthesis is due to DNA breakage, the results suggest that the breaks are induced at specific points.     

Genbank accession #: AJ237597

Plant Molecular Biology -     

Habitat selection and association of stream insects: a multivariate analysis

SUMMARY. Habitat selection and interspecies associations of stream insects were evaluated from a set of quantitative benthos samples and habitat measurements (velocity, depth, substrate, quantities of fine and leafy detritus) from a mountain stream. Substrate was characterized by an in situ grid method which effectively describes the size and distribution of the larger surficial materials within each sample unit. A principal components ordination of samples as characterized by abundance data over all species accounted for 54% of the total variance in three dimensions but implied continuous rather than discrete faunal change with habitat. Gradients in the habitat could not be identified with real confidence. Canonical correlation analysis identified three significant habitat-fauna interactions. The first corresponded to the gradient from eroding to depositing substrates and included detritus abundance, the second distinguished areas of fine from leafy detritus and the third appeared to include velocity-stone size interactions. A graphical technique based on ordination of physical data and clustering of associated species adequately summarized the distribution of five Ephemerella mayflies. The multivariate and interactive nature of stream bottom environments is discussed for problems involving prediction and experimental design and control.     

Retention of cryptic genes in microbial populations

Cryptic genes are silenced genes that can still be reactivated by mutation. Since they can make no positive contribution to the fitness of their carriers, it is not clear why many cryptic genes in microbial populations have not degenerated into useless DNA sequences. Hall et al. (1983) have suggested that cryptic genes have persisted because of occasional strong environmental selection for reactivated genes. The present mathematical study supports their suggestion. It shows that a cryptic gene can be retained without having any selective advantage over a useless DNA sequence, if selection for the reactivated gene occasionally occurs for a substantially long time.