Covalent structural modification of DNA-dependent RNA polymerase as a means for transcriptional control

Demonstration and partial characterization of ADP-ribosylation in Pseudomonas maltophilia

ADP-ribosylation of proteins occurs in many eukaryotes, and it is also the mechanism of action of a growing number of important bacterial toxins. To date, however, there is only one well-characterized ADP-ribosylation system where the ADP-ribosyltransferase and the substrate protein are both bacterial in origin, namely within the nitrogen-fixing bacterium Rhodospirillum rubrum. The present paper demonstrates the endogenous ADP-ribosylation of two proteins of Mr 32,000 and 20,000 within Pseudomonas maltophilia, a Gram-negative aerobe. The proteins have been partially purified: two apparently separate species of modified protein can be separated by ion-exchange chromatography and gel filtration (V0 and Mr 158,000 - Vi). The substrate protein(s) either has, or is co-eluted with, NAD+ glycohydrolase activity. The modification is mono-ADP-ribosyl in nature. The linkage between the acceptor amino acid and the ADP-ribose moiety is alkali-labile and stable to hydroxylamine, possibly indicating an S-glycosidic bond. The activity appears to be a true ADP-ribosylation reaction and not an NAD+ glycohydrolase activity followed by non-enzymic addition of ADP-ribose to protein. The results presented here indicate that ADP-ribosylation may have a wider significance within prokaryotic systems than previously thought.

Changed promoter specificity and antitermination properties displayed in vitro by bacteriophage T4-modified RNA polymerase

A 5.5 X 10(3) base-pair fragment of bacteriophage T4 DNA carrying genes 1, 3, 57, ipI and a cluster of transfer RNA genes was used as template for RNA polymerase isolated from uninfected Escherichia coli and from T4-infected bacteria. RNA transcripts were fractionated by gel electrophoresis and mapped by using as transcription template the 5.5 X 10(3) base fragment cleaved with different restriction enzymes. The comparison of the transcripts synthesized by the two RNA polymerases revealed a dramatic difference in their initiation specificities and abilities to utilize a transcription termination site. The T4-modified polymerase utilizes three new promoters on the template DNA fragment that are not utilized by the host enzyme. The modified enzyme, however, fails to produce some of the transcripts synthesized by the host RNA polymerase. The ability of T4-modified RNA polymerase to terminate transcription at a terminator present in the template DNA fragment is greatly reduced as compared to the unmodified host enzyme. The factors responsible for the new initiation and termination properties are associated with RNA polymerase core component. Analysis of RNA polymerase from bacteria infected with T4 mutants demonstrates that the new promoter specificity and the antitermination effect are caused by different factors.

RNA synthesis and poly(adenosine diphosphoribosyl) synthetase activity in developing mouse testis

RNA polymerase I and II and poly(ADP-ribosyl) synthetase activities were determined in isolated nuclei prepared from mouse testes at 1, 3, and 8 weeks after birth. RNA polymerase II and poly(ADP-ribosyl) synthetase activities increased with progression of spermatogenesis and age while RNA polymerase I activity decreased. The observed inverse relationship of RNA polymerase I and II parallels the shift in species of RNA, produced during spermatogenesis. Poly(ADP-ribosyl) synthetase activity increased with age, reaching a peak at 8 weeks. These enzymatic activities in aged mouse testis nuclei were equivalent to that of 8-week-old mice. Germ cells from the adult testis were separated by unit gravity velocity sedimentation. The enriched fractions containing pachytene and round spermatids possessed RNA polymerase and poly(ADP-ribosyl) synthetase activities. The present results suggest that transcriptional events during spermatogenesis may be modulated by changes in the activities of variants of RNA polymerase.

Control of promoter utilization by bacteriophage T4-induced modification of RNA polymerase alpha subunit

After infection of Escherichia coli cells, bacteriophage T4 induces several changes in the host DNA-dependent RNA polymerase. A well-characterized chemical change is a two-step ADP-ribosylation of the enzyme's alpha subunit (1). In order to investigate the effect of this change on RNA polymerase transcriptional properties in an in vitro system, we have reconstituted the enzyme from separated individual subunits which were obtained from normal or T4-modified RNA polymerases. It is demonstrated that the enzymes containing T4-modified alpha differ from the enzymes with normal alpha in two respects: (i) their overall activity on T4 DNA is reduced and (ii) they fail to utilize certain T4 promotors while efficiently utilizing other promoters. Among the promoters which are switched off by alpha modification are the two promoters of the D region and one of the two promoters of the T4 tRNA gene cluster. The differential effect of alpha modification on the expression of the tRNA and the D regions in vitro correlates with the previously established pattern of their transcription in vivo. It is suggested that the T4-induced ADP-ribosylation of RNA polymerase alpha subunit is involved in the shutoff of the early bacteriophage genes at the late stage of phage development.