S. Laalami et al., IN-VIVO STUDY OF ENGINEERED G-DOMAIN MUTANTS OF ESCHERICHIA-COLI TRANSLATION INITIATION-FACTOR IF2, Molecular microbiology, 11(2), 1994, pp. 293-302
During the IF2-catalysed formation of the 30S initiation complex, the
GTP requirement and its subsequent hydrolysis during 70S complex forma
tion are considered to be essential for translation initiation in Esch
erichia coil in order to clarify the role of certain amino acid residu
es believed to be crucial for the GTP hydrolytic activity of E. coil I
F2, we have introduced seven single amino acid substitutions into its
GTP-binding site (GIy for Val-400; Thr for Pro-446; Gly, Glu, Gln for
His-448; and Asn, Glu for Asp-501). These mutated IF2 proteins were ex
pressed in vivo in physiological quantities and tested for their abili
ty to maintain the growth of an E. coil strain from which the function
al chromosomal copy of the infB gene has been deleted. Only one of the
mutated proteins (Asp-501 to Glu) was able to sustain cell viability
and several displayed a dominant negative effect. These results emphas
ize that the amino acid residues we substituted are essential for the
IF2 functions and demonstrate the importance of GTP hydrolysis in tran
slation initiation. These findings are discussed in relation to a prev
iously proposed theoretical model for the IF2 G-domain.