FIG. 1.

Spectra of spontaneous ac mutations in rnh⁺ (above sequence) and rnhΔ (below sequence) genetic backgrounds. Capital letters indicate base pair substitutions, boldface indicates insertions, and lowercase letters indicate deletions. The sequence is the ac gene from ATG (positions 1 through 3) encoding the initiation codon through TAA (positions 153 to 156) encoding the ochre termination codon; every 10th base is underlined and numbered beneath when possible. When an insertion or deletion could have arisen between two or more short repeated sequences, the mutation is placed in the middle of the wild-type repeats. Two or more adjacent added or deleted bases represent a single mutation, and repeated mutations are stacked. There are no complex mutations containing mixtures of base pair substitutions, insertions, and/or deletions. Note that several mutations are not shown: deletions of 32 bases between TTTT at 59 through 62 and at 91 through 94 that occurred three times in rnh⁺ and twice in rnhΔ and one addition of 99 bases that occurred once in rnhΔ (see text).