ADP-ribosylation of Nonhistone Chromatin Proteins in Vivo and of Actin in Vitro and Effects of Normal and Abnormal Growth Conditions and Organ-specific Hormonal Influences

Abstract

In contrast to a large variety of covalent modifications of both histone and nonhistone proteins by phosphorylation, acetylation, methylations etc., reactions that appear to exhibit a relatively broad selectivity, poly ADP-ribosylation by (ADP-R)n in small rodents in vivo is confined to an extent of at least 99% to nonhistone chromosomal proteins, as determined by an (ADP-R)n > 4 specific IgG antiserum assay (Minaga et al. 1979). Similar results were recorded in another laboratory in varying biological material by different experimental methods (Bradehorst et al. 1978; Bradehorst et al. 1979). It should be noted that ADP-ribosylation of histone H1 in vitro is readily demonstrable when larger quantities of the ADP-R acceptor histone H1 are added to the purified poly ADP-R synthetase (Kawaichi et al. 1980), but this is a typical in vitro enzymological result. Quantitatively misleading results can be obtained in vivo or, in cell cultures, when only radiochemical assays of ADP-R are the basis of analyses without consideration of the absolute quantities of (ADP-R)n (Giri et al. 1978; Jump et al. 1979). It is obvious that measurement of radioactivity alone does not distinguish between small quantities of highly radioactive (ADP-R)n or larger amounts of (ADP-R)n with lower specific activity, both parameters being related to turnover (Kun et al. 1979). There is no doubt that only about 0.1% to 0.6% of the total (ADP-R)n > 4 is associated in vivo with histones and shorter as well as longer homopolymers exist as covalent complexes with histones (Minaga et al. 1979). However, the overwhelming targets of ADP-ribosylation are nonhistone proteins that have been identified by the pioneering experiments of Paul and Gilmour (1968) to play an as yet not well understood role in the regulation of differentiated cellular functions in eukaryotes. The previously proposed correlation between transcriptionally active chromatin and the degree of ADP-ribosylation (Mullins et al. 1977) is presently doubtful, since more recently no connection was found between the localization or activity of poly ADPR polymerase and transcriptional activity of chromatin (Yukioka et al. 1978).