(a) Promoter :
It is a gene that lies near operator which functions as binding site structural genes if operator allows.
(b) tRNA :
Functions as adapter molecule that picks up a particular amino – acid from cellular pool and takes same over A site, m – RNA for incorporation into polypeptide.
(c) Exons :
Coding segments present in primary transcript which on splicing by snRNP’s get joined to form functional m-RNA.