Figure 6.

Human SBP2 interacts with the 60S ribosomal subunit. (A) Detection of hSBP2 in sucrose gradient fractions of 60S and 40S ribosomal subunits. TCA-precipitated fractions were resolved by SDS–PAGE and assayed by western blot with an anti-hSBP2 antibody (lanes 1 and 2). hSBP2 FL is the full-length human SBP2, p40 (lane 4) a 40S ribosomal subunit protein used as the control. (B) hSBP2 deletion mutant proteins were assayed for ribosome binding. Fractions containing 60S bound hSBP2 were treated as in (A). Nomenclature as in (A) and Figure 5A. The lower panel (input proteins) is a western blot showing that the mutant proteins were indeed expressed and detectable by the anti-SBP2 antibody. The arrow points to a cross-reaction product arising from an E.coli protein. (C) The 60S-bound alanine scanning mutant proteins (shown in Figure 5B) were analyzed as in (A). Lane 1: hSBP2FL detected by western blot before gradient loading. The single and double asterisks denote frequently encountered hSBP2 proteolysis fragments. The lower panel (input proteins) serves the same purpose as in (B).