lacZY+ fusions in Escherichia coli

Abstract
The nucleotide sequence of 3 lacZ--Y+ fusions found among spontaneous lacY+ revertants of the lacY- mutant MAB16 in E. coli is reported. MAB16 is a frameshift mutation in codon 6 of the lacY gene. DNA sequence analysis of the fusions shows the first 8 N-terminal codons of the lacY gene can be replaced by 3, 39 or 804/805 N-terminal codons of the lacZ gene without impairing lac permease activity qualitatively.