MODULATION OF THE P1 PLASMID PARTITION PROTEIN PARA BY ATP, ADP, AND P1 PARB

ParA is an essential P1 plasmid partition protein. It represses transc ription of the par genes (parA and parB) and is also required for a se cond, as yet undefined step in partition. ParA is a ParB-stimulated AT Pase that binds to a specific DNA site in the par promoter region, ATP binding and hydrolysis by ParA affect ParA activities in vitro. ATP a nd ADP binding stimulate ParA DNA binding and dimerization; however, A TP hydrolysis has a negative effect on DNA binding. Our current experi ments reveal that ATP binding and hydrolysis affect ParA conformation and ParA sensitivity to ParB, Nucleotide binding assays show that ParA binds ATP better than ADP (K-d values of 33 and 50 mu M, respectively ), Interaction with these nucleotides as well as ATP hydrolysis by Par A alter ParA conformation as established by CD and ParA sensitivity to heat denaturation. Finally, we show that ParB stimulates ParA DNA bin ding, This stimulation requires ATP hydrolysis in vitro, suggesting th at one role for ATP hydrolysis in vivo is to make ParA repressor sensi tive to ParB, Our observations lead to the suggestion that ATP binding and hydrolysis have separable roles in ParA repressor function and pe rhaps in ParA partition functions as well.