Distribution of CAP and methylated nucleotides between the RNase sensitive and resistant fractions of mRNA in messenger ribonucleoprotein particles.

When polyribosomal mRNP is exposed to ribonucleases most but not all of the mRNA is converted to acid soluble products. If mRNP is prepared under isotonic conditions there are two types of ribonuclease resistant core fractions, one which contains the poly(A) part of the mRNA and a second which contains mRNA fragments, 30-40 nucleotides in length. Like poly(A) these fragments appear to be protein associated in the mRNP complex. Non-poly(A) fragments in mRNP prepared from adenovirus-infected cells harvested in the late phase of infection contained only 3% of CAP structures and 12% of internally located methylated nucleotides. This indicates that no CAP structures but one out of the seven internally located methylated nucleotides found in the mRNA are situated in protein associated regions.