Affinity labelling of rat liver ribosomal protein S26 by heptauridylate containing a 5'-terminal alkylating group.

Heptauridylate bearing a radioactive alkylating [14C]-4-(N-2-chloroethyl-N-methylamino)benzylamine attached to the 5'-phosphate via amide bond, was bound to ribosomes and small ribosomal subunits from rat liver which thereby were coded to bind N-acylated Phe tRNA. After completion of the alkylating reaction and subsequent hydrolysis of the phosphamide bond ribosomal proteins were isolated. Radioactivity was found covalently associated preferentially with protein S26 and, to a very small extent, with proteins S3 and S3a. The affinity labelling reaction could be abolished by (pU)14 and poly(U). From the results it is concluded that ribosomal protein S26 is located at the mRNA binding site of rat liver ribosomes.