This family consists of several bacterial conjugative transfer TraP proteins from Escherichia coli and Salmonella typhimurium. TraP appears to play a minor role in conjugation and may interact with TraB, which varies in sequence along with TraP, in order to stabilise the proposed transmembrane complex formed by the tra operon products [1].

1: Analysis of the traLEKBP sequence and the TraP protein from three F-like plasmids: F, R100-1 and ColB2. Anthony KG, Kathir P, Moore D, Ippen-Ihler K, Frost LS; J Bacteriol 1996;178:3194-3200. PMID:8655498