Multiple effects of an RNA polymerase beta' mutation on in vitro transcription

Susceptibility of human foetal brain tissue to cool- and freeze-storage

Human second trimester foetal brain tissue was stored for a period of 1-6 weeks under various conditions in an attempt to evaluate factors influencing its susceptibility (cell loss) and survivability. Post-storage viability of mesencephalon, striatum, cerebellum and occipital cortex was assessed by a protocol combining vital staining with cell density counts so that tissue viability and cell loss could be evaluated simultaneously; tissue survivability was evaluated by cell culture. A significant amount of cell loss occurred after 24 h storage at room temperature, after one week at 4 degrees C and by two weeks at -20 degrees C in all structures; storage at -196 degrees C resulted in 17-21% cell loss at the end of a 6 week period. At -20 degrees C the cryoprotective effect of 20% FCS was equivalent to that of 15% FCS + 7% DMSO combined, suggesting potential use of serum in replacement of chemical additives. The procedure for removal of DMSO was critical to cell viability and survivability: single step dilution led to 27-39% greater cell loss than slow, multi-step dilutions. In comparison to fresh, non-stored tissue, immunocytochemical characterization of in vitro propagated stored tissue revealed no changes in the populations of major constituent cell types including neurones, dopaminergic neurones, glial and fibroblast cells. These results provide information on possible conditions under which transplant tissue can be satisfactorily stored depending on the prevailing requirements.

Salmonella typhimurium rpoB and rpoC genes cloned on lambda phages

Salmonella typhimurium rpoB and rpoC genes, coding for the RNA polymerase subunits beta and beta', respectively, were isolated on lambda phages. Like their E. coli counterparts the two genes are closely linked and probably share a common promoter. The distribution of the target sites for several restriction enzymes, however, shows considerable divergence from the E. coli pattern.

Cold-sensitive mutations in beta and beta' subunit gene affecting the interaction of RNA polymerase with promoters

RNA polymerases with a cold-sensitive activity were purified from seven mutants of Escherichia coli. Subunit reconstitution experiments have shown that RNA polymerases from three mutants (Rpob262, RpoB264, and RpoB265) owed their cold sensitivity to alterations in the beta subunit. Three mutants (RpoC3, RpoC263, and RpoC267) were shown to be defective in the beta' subunit and one (RpoBC266) in both beta and beta' subunits. Two mutations (rpoC3 and rpoC263) reduced the level of RNA polymerase reconstitution. RNA polymerases from RpoC3 and RpoBC266 mutants are defective in RNA chain elongation at 6 degree C, while all the other mutants are defective in RNA polymerase-promoter interaction. most mutant RNA polymerases differ from the wild-type enzyme in transcription selectivity. The results obtained in this study indicate that both beta and beta' subunits are involved in RNA chain elongation and promoter binding and selection.

A cold-sensitive beta subunit mutant RNA polymerase from Escherichia coli with defects in promoter opening in vitro

A cold-sensitive mutation in the rpoB gene for the RNA polymerase beta subunit increasing the temperature of promoter opening on T2 phage DNA was obtained in Escherichia coli. The mutation also affects the stages preceding promoter opening by increasing the dissociation rate of RNA polymerase--DNA closed complexes. The affinity of RNA polymerase to T2 and lambda DNA is differentially changed by the mutation. The relative efficiency of transcription of these two templates is also changed. These results suggest a participation of the RNA polymerase beta subunit in the interaction with promoters.