Table 1.

Association rate constants of 50S subunits with 30S:mRNA in the presence of different combinations of Initiation Factors and fMet-tRNA.

Factors added	kass(μM-1s-1)
none	1.2 ± 0.13
+IF3	<0.0
+IF1+IF2:GTP	4.1 ± 0.3
+IF1+IF2:GTP+IF3	< 0.01
+IF1+IF2:GTP+IF3+fMet-tRNA	12.2 ± 1.6
+IF1+IF2:GTP+IF3+fMet-tRNA (*)	8.6 ± 1.2
+IF1+IF2:GDP+IF3+fMet-tRNA (*)	0.13 ± 0.03
The association rate constant kass was calculated as an average (kav ) over rate constants (ki ) obtained from n (between six and eight) individual time traces of light scattering in a stopped-flow experiment. The error is the standard deviation σ obtained from the variance, estimated as
(*) The reaction buffer contained 1 mM phosphoenolpyruvate (PEP).