The following article requires a subscription:



(Format: HTML, PDF)

Summary: Pkn8 is a membrane-associated protein Ser/Thr kinase (PSTK) of Myxoccocus xanthus that was previously found to associate with a novel cytoplasmic kinase, Pkn14. In the present study, MrpC, an essential transcription factor for fruA expression during fruiting body development, was identified using a genomic yeast two-hybrid screen with Pkn14 as bait. Our biochemical studies demonstrated that purified Pkn8 and Pkn14 are active kinases and that Pkn8 is able to phosphorylate Pkn14 that forms a tetramer via its C-terminal 41 residues. Moreover, Pkn14 phosphorylated purified MrpC, indicating that Pkn8 is a Pkn14 kinase and Pkn14 is an MrpC kinase. The pkn8 and pkn14 deletion strains ([DELTA]pkn8 and [DELTA]pkn14) developed into fruiting bodies significantly faster than that of the parent strain, DZF1. While mrpC expression was at a low level in DZF1 during vegetative growth, it was highly elevated in [DELTA]pkn8 and [DELTA]pkn14 during vegetative growth and development. Furthermore, FruA, usually induced at 6 h of development, was instead detected at the early stationary phase and accumulated faster during development in [DELTA]pkn8 and [DELTA]pkn14. Therefore, the developmental phenotype of [DELTA]pkn8 and [DELTA]pkn14 seems to be due to untimely FruA production mediated by elevated levels of MrpC in [DELTA]pkn8 and [DELTA]pkn14 during vegetative growth. As pkn14 expression was increased at the mid- and late-log. phases in DZF1 but decreased during development, the Pkn8-Pkn14 kinase cascade appears to negatively regulate mrpC expression by phosphorylating MrpC during vegetative growth. This is the first demonstration of a functional PSTK cascade in prokaryotes. mrpC expression has been proposed to be activated by MrpA and MrpB which belong to a two-component His-Asp phosphorelay signal transduction system and that MrpC autoregulate its own expression (Sun H. and Shi W., 2001 J Bacteriol 183: 4786-4795). Therefore, M. xanthus seems to utilize both eukaryotic PSTK cascade and prokaryotic His-Asp phosphorelay system to precisely regulate mrpC expression with specific timing during development.

Copyright (C) 2005 Blackwell Publishing Ltd.