Protein A24 lyase activity in nucleoli of thioacetamide-treated rat liver releases histone 2A and ubiquitin from conjugated protein A24

Abstract
Isolated liver nucleoli from rats treated for 3 days with thioacetamide contained an enzyme activity which specifically degraded conjugate protein A24. Two-dimensional polyacrylamide gel electrophoresis indicated that the amount of protein A24 in chromatin decreased during incubation at 37.degree. C for 60 min with these nucleoli. A marked increase was found in the content of free ubiquitin, the nonhistone component of protein A24. Incubation of 3H-labeled protein A24 with the thioacetamide-treated liver nucleoli resulted in the linear release of 3H-labeled histone 2A and 3H-free ubiquitin in the presence of phenylmethanesulfonyl fluoride (PMSF) for 2 h. Pretreatment of the nucleoli with trypsin or by heating at 80.degree. C for 10 min inhibited their ability to cleave protein A24. Protein A24 lyase catalyzes the reaction: protein A24 .fwdarw. histone 2A + ubiquitin.

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