Lysine 188 of the catabolite gene activator protein (CAP) plays no role in specificity at base pair 7 of the DNA half site.
Two similar, but not identical, models have been proposed for the amino acid-base pair contacts in the CAP-DNA complex ('model I,' Weber, I. and Steitz, T., Proc. Natl. Acad. Sci. USA, 81, 3973-3977, 1984; 'model II,' Ebright, et al., Proc. Natl. Acad. Sci. USA, 81, 7274-7278, 1984). The most important difference between the two models involves Lys188 of CAP. Model I predicts that Lys188 of CAP makes a specificity determining contact with base pair 7 of the DNA half site. In contrast, model II predicts that Lys188 makes no contact with base pair 7 of the DNA half site. In the present work, we have used site-directed mutagenesis to replace Lys188 of CAP by Asn, an amino acid unable to make the putative contact. We have assessed the specificities of the following proteins, both in vitro and in vivo: wild-type CAP, [Asn188]CAP, [Val181]CAP, and [Val181;Asn188]CAP. The results indicate that Lys188 makes no contribution to specificity at base pair 7 of the DNA half site. We propose, contrary to model I, that Lys188 makes no contact with base pair 7 of the DNA half site.
Ebright
R H
RH
Department of Chemistry, Rutgers University, New Brunswick, NJ 08855.
Gunasekera
A
A
Zhang
X P
XP
Kunkel
T A
TA
Krakow
J S
JS
D001483:Base Sequence; D001665:Binding Sites; D003090:Coliphages / Q000235:genetics; D002373:Cyclic AMP Receptor Protein / Q000235:genetics / Q000378:metabolism*; D004247:DNA / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D008239:Lysine; D008969:Molecular Sequence Data; D009154:Mutation; D011485:Protein Binding
D002373:Cyclic AMP Receptor Protein; D004247:DNA; D008239:Lysine