PCB 3063 Lecture Notes - Lecture 40: Transesterification, Autocatalysis, Consensus Sequence
Document Summary
What are the 5 steps of an addition of 5" cap: one of the three phosphate groups at the 5" of mrna is removed, a guanine nucleotide with its phosphate group is added. 3. methyl groups are added to the 7 position of the base of the terminal guanine nucleoside. 4. methyl groups are also added to the 2" position of the sugar on the second and third nucleotide. 5. the base on the initial nucleotide may also be methylated. Removed by a nuclear machinery that identifies a short consensus sequence at the exon-intron boundary in the pre-mrnas. A free guanosine nucleotide cofactor: gtp, gdp, or gmp. 1st transfer: the free 3" -oh of a free guanosine nucleotide cofactor attacks the 5" end of the intron. 2nd transfer: the free 3" -oh of exon 1 attacks the 5"p of exon 2; the linear intron is released and the exons are joined. Small nuclear ribonucleoproteins that contain small nuclear rnas.