CORRELATION OF CHI ORIENTATION WITH TRANSCRIPTION INDICATES A FUNDAMENTAL RELATIONSHIP BETWEEN RECOMBINATION AND TRANSCRIPTION

Cross-over hot-spot instigator (Chi) sequences (5'-GCTGGTGG-3') are ab undant, strand-specific, sequences, which locally increase recombinati on in Escherichia coli. Located within G-rich 'recombination islands', Chi orientations correlate with the orientations both of DNA. replica tion and of transcription. Consistent with evidence from eukaryotic sy stems for a fundamental relationship between recombination and transcr iption, we find for E. coli Chi sequences, and for Haemophilus influen zae Chi-like sequences, that orientations correlate better with transc ription than with replication. Complying with Szybalski's transcriptio n direction rule, open reading frames in these prokaryotes have purine -rich mRNA-synonymous DNA strands. Hence, the G-richness of 'recombina tion islands' may reflect their correspondence with 'transcriptional i slands' (genes). Comparison of a natural with the corresponding shuffl ed sequence, indicates a base order-dependent island unit of approx. 1 kb. (C) 1998 Elsevier Science B.V. All rights reserved.