PROTEIN ENVIRONMENT OF TEMPLATE IN DECODING AREA EXAMINED BY AFFINITYMODIFICATION OF HUMAN PLACENTAL RIBOSOMES WITH ALKYLATING DERIVATIVESOF OLIGORIBONUCLEOTIDE PGUGU(3)

Affinity modification of human placental 80S ribosomes was performed u sing an alkylating mRNA analog, oethyl)-N-methylamino]benzylmethyl-5'- phosphoamide derivative of pGUGU(3) that contains codons for valine (G UG) and phenylalanine (UUU). Upon modification, the ribosomes were use d as complexes with Val-tRNA(Val) or Phe-tRNA(Phe), complexes with two tRNA molecules, as well as binary complexes without tRNA. In all case s, mainly small subunits (mostly protein components) were alkylated, e xcept for the complex with Val-tRNA(Val) where both 18S rRNA and prote ins were modified to a comparable extent. The extent of modification o f 40S subunits in binary complexes was substantially smaller than in t ile presence of related tRNA. In complexes with Phe-tRNA(Phe) and with two tRNA molecules, S26 protein was the main target of alkylation; S6 protein was only slightly modified. In the absence of tRNA, only S6 w as modified, whereas in the complex with Val-tRNA(Val) both S6 and S6 were modified, albeit the latter to a smaller extent.