Ribosomal proteins cross-linked to natural mRNA by UV irradiation of rat liver polysomes

After rat liver polysomes were irradiated with UV light at 254 nm for 2 h, a cross-linked poly(A)-containing mRNA-protein complex (mRNP) was prepared and a protein moiety was labeled with 125I. After RNase treatment, its protein moiety was analyzed by two-dimensional polyacrylamide gel electrophoresis followed by radioautography. There were radioactive spots which extended from the positions of those of S3/S3a, S6, L5, and L6/L7 towards the origin. In the case of UV irradiation for 30 min, radioactive spots extending similarly from those of S3/S3a, and L5 were observed. Radioactive areas on the two-dimensional gel in the case of irradiation for 2 h were further analyzed by SDS polyacrylamide gel electrophoresis. The peaks of radioactivity were detected at the protein band containing L6, that containing S3a and L5 and that containing S6, L7, and L8. It was proposed that S3a, S6, L5, and L6 proteins, according to the proposed uniform nomenclature (McConkey et al. (1979) Mol. Gen. Genet. 169, 1-6(1)), were cross-linked to mRNA by UV irradiation.