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Biochim Biophys Acta. 2003 Mar 21;1646(1-2):86-99.

Subdomain organization and catalytic residues of the F factor TraI relaxase domain.

Author information

1
Department of Biology, The Johns Hopkins University, 3400 N. Charles St., Baltimore, MD 21218, USA.

Abstract

TraI from conjugative plasmid F factor is both a "relaxase" that sequence-specifically binds and cleaves single-stranded DNA (ssDNA) and a helicase that unwinds the plasmid during transfer. Using limited proteolysis of a TraI fragment, we generated a 36-kDa fragment (TraI36) retaining TraI ssDNA binding specificity and relaxase activity but lacking the ssDNA-dependent ATPase activity of the helicase. Further proteolytic digestion of TraI36 generates stable N-terminal 26-kDa (TraI26) and C-terminal 7-kDa fragments. Both TraI36 and TraI26 are stably folded and unfold in a highly cooperative manner, but TraI26 lacks affinity for ssDNA. Mutational analysis of TraI36 indicates that N-terminal residues Tyr(16) and Tyr(17) are required for efficient ssDNA cleavage but not for high-affinity ssDNA binding. Although the TraI36 N-terminus provides the relaxase catalytic residues, both N- and C-terminal structural domains participate in binding, suggesting that both domains combine to form the TraI relaxase active site.

PMID:
12637015
DOI:
10.1016/s1570-9639(02)00553-8
[Indexed for MEDLINE]

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