The chvH locus of Agrobacterium encodes a homologue of an elongation factor involved in protein synthesis

The virulence of Agrobacterium tumefaciens depends on both chromosome- and Ti plasmid-encoded gene products. In this study, we characterize a chromoso mal locus, chvH, previously identified by TnphoA mutagenesis and shown to b e required for tumor formation. Through DNA sequencing and comparison of th e sequence with identified sequences in the database, we show that this loc us encodes a protein similar in sequence to elongation factor P, a protein thought to be involved in peptide bond synthesis in Escherichia coli. The a nalysis of vir-lacZ and vir-phoA translational fusions as well as Western i mmunoblotting revealed that the expression of Vir proteins such as VirE2 wa s significantly reduced in the chvH mutant compared with the wild-type stra in. The E. coli efp gene complemented detergent sensitivity, virulence, and expression of VirE2 in the chvH mutant, suggesting that chvH and efp are f unctionally homologous. As expected, ChvH exerts its activity at the posttr anscriptional level. Southern analysis suggests that the gene encoding this elongation factor is present as a single copy in A. tumefaciens. We constr ucted a chvH deletion mutant in which a 445-bp fragment within its coding s equence was deleted and replaced with an omega fragment. On complex medium, this mutant grew more slowly than the wild-type strain, indicating that el ongation factor P is important but not essential for the growth of Agrobact erium.