There
are three principles to keep in mind when predicting the sequence of
the mRNA produced by transcription of a particular DNA sequence. The RNA polymerase reads the sequence of DNA bases from only one of the two strands of DNA: the template strand.The
RNA polymerase reads the code from the template strand in the 3' to 5'
direction and thus produces the mRNA strand in the 5' to 3' direction.In
RNA, the base uracil (U) replaces the DNA base thymine (T). Thus the
base-pairing rules in transcription are A→U, T→A, C→G, and G→C, where
the first base is the coding base in the template strand of the DNA and
the second base is the base that is added to the growing mRNA strand.</span>
