VIBRIO-CHOLERAE HCP, A SECRETED PROTEIN COREGULATED WITH HLYA

Hcp is a 28-kDa secreted protein of Vibrio cholerae regulated coordina tely,vith the hemolysin, HlyA. Both proteins show a dependence on HlyU for expression, suggesting that Hcp may be secreted by V, cholerae in vivo, We have identified and sequenced two genes for Hcp, designated hcpA and hcpB (hemolysin-coregulated protein), The genes encode identi cal amino acid sequences, Both express a 28-kDa protein, despite open reading frames with only a 19-kDa capacity, suggesting that the Hcp pr otein runs aberrantly on polyacrylamide gel electrophoresis, There is no cleavage involved in secretion of Hcp from the cell, suggesting a n ovel mechanism of secretion, An hcp null mutant was constructed, and t his strain displayed no deficiency in virulence or colonization in the infant mouse cholera model, From sequence data and primer extension a nalysis, we predict that the hcp promoter is the sigma(54) type, with a candidate integration host factor binding site upstream, Although hc p and hlyA are coregulated by HlyU, there are no obvious similarities between their promoters, We predict that an intermediate regulator may be involved in the activation of hcp by HlyU, This raises the possibi lity that HlyU is part of a regulatory cascade.