NUCLEOTIDE G-1207 OF 18S RIBOSOMAL-RNA IS AN ESSENTIAL COMPONENT OF THE HUMAN 80S RIBOSOMAL DECODING CENTER

mRNA analogues-derivatives of oligoribonucleotides consisting of two d ifferent codons and bearing an aryl azide group at the 5'-phosphates-w ere crosslinked to human 80S ribosomes by UV-irradiation of the variou s model complexes obtained in the presence of the cognate tRNAs. Three sequences, namely PUUUGUU (coding for Phe and Val), PUUCUAAA (first t riplet coding for Phe and second being stop-codon), and pGUGUUU (codin g for Val and Phe), have been used. Sequences of 18S rRNA containing n ucleotides crosslinked to the mRNA analogues were examined by hydrolys is with RNase H in the presence of various cDNA probes. Crosslinked nu cleotides were identified by primer extension. In all cases, only nucl eotide G-1207 (equivalent to G-926 in Escherichia coli 16S rRNA) has b een detected as crosslinked. Crosslinking of the mRNA analogues to the large ribosomal subunit was negligible.