A new class of proteins regulating gene expression in enterobacteria

Abstract
YmoA and Hha are highly similar bacterial proteins downregulating gene expression In Yersinia entero-colitlca and Escherichia coli. respectively. The pheno-type of ymoA mutants evokes that of mutants affected in some histone-like proteins. This paper describes complementation of a ymoA mutation in Y. enterocolitica by the hha gene from E. coli. We show that YmoA and Hha are not only very similar proteins but that they are functionally Interchangeable. Genetic experiments indicate that Hha can also stimulate transposition events in vivo. By Southern Biol analysis we detected hha-homologous genes at least in Citrobacter diversus, Shigella flexneri, Shigella dysenteriae, Klebsiella pneumoniae and Salmonella typhimurium. We suggest that both YmoA and Hha belong to a new family of proteins down regulating gene expression in different enterobacteria.