Pre-Mrna

The first (primary) transcript from a protein coding gene is often called a pre-mRNA and contains both introns and exons. Pre-mRNA requires splicing (removal) of introns to produce the final mRNA molecule containing only exons.

Mesomere

Blastomere exhibiting a size intermediate between a macromere and a micromere.

Attenuator Stem

A configuration of the leader transcript that signals transcription termination in attenuator-controlled amino acid operons.