Question

We are discussing the initiation process of transcription. The instructor said that "the first ribonucleoside triphosphate (rNTP) of the new RNA chain is usually a purine (A or G)."

I don't understand what this means. Can someone explain it in simple terms? Does it mean that the first letter of the new transcribed mRNA molecule usually starts with a A or G?

Answer 1

The poorest initiating nucleotide is CTP to start new RNA chain and a very good initiating nucleotide is GTP to start new transcripts. E coli promoters shows frequencies for selecting transcription initiating nucleotides as A [47%], G [28%], T [15%], and C [10%] which suggest that most transcripts start with efficient initiating nucleotides to maximize transcript synthesis. It also raise the possibility that particular initiating nucleotides are evolutionarily selected to control transcript levels, which may be particularly important for low-abundance transcripts.