AMHERST, Mass. Usually indigestion is a bad thing, but experiments by researcher Peter Chien and graduate student Robert Vass at the University of Massachusetts Amherst recently showed that for the bacteria Caulobacter crescentus, partial degradation of a DNA replication protein is required to keep it alive.
DNA replication is one of the most highly controlled biological processes in all organisms, says Chien, an assistant professor of biochemistry and molecular biology at UMass Amherst. From humans all the way back to bacteria, all cells must faithfully duplicate their genomes in order to survive. To coordinate the start, ensure the completion and repair damages during DNA replication, specialized proteins play a key role by regulating processes.
In work published this month in Proceedings of the National Academy of Sciences, Chien and Vass report that one of these specialized replication factors, DnaX, is, to their surprise, partially digested or trimmed, physically cut into shorter fragments, by an energy-dependent protease known as ClpXP, which generates specific-sized fragments that are essential for Caulobacter's normal growth.
The phenomenon isn't entirely unknown, Chien explains. Short as well as long versions of DnaX had been observed 20 years ago in another bacteria, E. coli. But in E. coli, the short form was produced by changes in translation due to an early ribosome stop at a specific RNA sequence. That RNA sequence is absent in many bacteria DnaX genes including in Caulobacter, so scientists long thought that short DnaX only existed in bacteria like E. coli.
Based on previous studies in his lab, Chien and Vass moved on to investigate, by purifying these proteins and testing their activity in Caulobacter in vivo, whether the protein DnaX could be degraded by the protease ClpXP. To their surprise, ClpXP did recognize DnaX, but only partially degraded
|Contact: Janet Lathrop|
University of Massachusetts at Amherst