This is a subdomain found in TraI present in E. coli. Tra1 is a conjugative relaxase that forms part of the Type IV secretion system. This subdomain, referred to as 2A, is located in N-terminal region of the translocation signal (TSA) domain. TSA is known to reside in a larger ssDNA-binding domain [1].

1: Structure of a translocation signal domain mediating conjugative transfer by type IV secretion systems. Redzej A, Ilangovan A, Lang S, Gruber CJ, Topf M, Zangger K, Zechner EL, Waksman G; Mol Microbiol. 2013;89:324-333. PMID:23710762