Splicing of Xenopus laevis ribosomal protein RNAs is inhibited in vivo by antisera to ribonucleoproteins containing U1 small nuclear RNA.

The activity of antisera against ribonucleoproteins containing U1 small nuclear RNA (Sm and RNP) has been analysed on pol II transcripts in an in vivo system. Xenopus laevis ribosomal protein gene transcripts are accumulated in the form of precursor RNA when either of the two kinds of antisera are injected into the germinal vesicles of X. laevis oocytes before the injection of purified L1 and L14 ribosomal protein genes. No effect on the accumulation of mature histone mRNA is detected when X. laevis histone genes are injected together with the RNP antiserum. These results strongly suggest that U1-RNP complexes play an essential role in intron removal in vivo.