Genetic fusions defining trp and lac operon regulatory elements.

Two procedures for easily isolating deletions that fuse the trp and lac operons are described. Using these procedures, a large number of fusion deletions have been isolated. The 1a.c ends of these deletions extend varying distances into the &I gene and the Z&c promoter-operator region. Therefore, contrary to a previous report, there does not appear to be a messenger-termination signal at the Cterminal end of the 1acI gene. The trp ends of fusion deletions do not have to extend into the trp structural genes to effect fusion, suggesting that mRNA synthesis initiated at the trp promoter proceeds some distance beyond the trp structural genes before a messenger termination signal is reached. Deletions that ext’end a short distance into the C-terminus of trpA, the last gene in the trp operon, do not, completely abolish activity of the trpA product. The procedures described for isolating fusions of the trp and Zac operons can be generalized to other systems.