[Nuclear RNP, containing pre-mRNA. XIV. Nature of particles, containing 5'- and 3'-end structures]

Some characteristic peculiarities of the 5'-end and 3'-end structures of pre-mRNA isolated from nuclear RNP particles have been investigated: presence of triphosphorylated nucleotides on the 5'-ends, as a characteristic of the primary product of transcription; presence of modified 5'-ends -- blocked and methylated structures -- caps; presence of poly(A) blocks attached to the 3'-end of pre-mRNA during post-transcriptional transformation of the latter. It was shown that pre-mRNA isolated from nuclear RNP particles contained triphosphorylated nucleotides as well as a "cap" structure at the 5'-ends. On the 3'-ends of pre-mRNA from nuclear RNP particles isolated in the presence of a RNAse inhibitor, the presence of poly(A) blocks have been shown. These poly(A) structures are separated very easily from pre-mRNA during mild RNAase digestion. This is the reason why they are not detected in 30S monoparticles, containing pre-mRNA fragments connected with one informofer. Almost all poly(A) complexes in this condition are combined with proteins and have the sedimentation coefficient of about 14S. It was concluded that formation of nuclear pre-mRNA containing RNP-particles take place just after the onset of RNA synthesis. All processing steps occur with pre-mRNA packed in nuclear RNP particles.