This family contains several Bacillus thuringiensis P21 proteins. These proteins are thought to be molecular chaperones and have mosquitocidal properties [1,2].

1: A 20-kilodalton protein is required for efficient production of the Bacillus thuringiensis subsp. israelensis 27-kilodalton crystal protein in Escherichia coli. Adams LF, Visick JE, Whiteley HR; J Bacteriol 1989;171:521-530. PMID:2644205

2: Identification of a gene for Cyt1A-like hemolysin from Bacillus thuringiensis subsp. medellin and expression in a crystal-negative B. thuringiensis strain. Thiery I, Delecluse A, Tamayo MC, Orduz S; Appl Environ Microbiol 1997;63:468-473. PMID:9023925