Host requirements for growth of lambda-P22 hybrid in Escherichia coli

A CI-independent form of replicative inhibition: turn off of early replication of bacteriophage lambda

Several earlier studies have described an unusual exclusion phenotype exhibited by cells with plasmids carrying a portion of the replication region of phage lambda. Cells exhibiting this inhibition phenotype (IP) prevent the plating of homo-immune and hybrid hetero-immune lambdoid phages. We have attempted to define aspects of IP, and show that it is directed to repλ phages. IP was observed in cells with plasmids containing a λ DNA fragment including oop, encoding a short OOP micro RNA, and part of the lambda origin of replication, oriλ, defined by iteron sequences ITN1-4 and an adjacent high AT-rich sequence. Transcription of the intact oop sequence from its promoter, p(O) is required for IP, as are iterons ITN3-4, but not the high AT-rich portion of oriλ. The results suggest that IP silencing is directed to theta mode replication initiation from an infecting repλ genome, or an induced repλ prophage. Phage mutations suppressing IP, i.e., Sip, map within, or adjacent to cro or in O, or both. Our results for plasmid based IP suggest the hypothesis that there is a natural mechanism for silencing early theta-mode replication initiation, i.e. the buildup of λ genomes with oop(+)oriλ(+) sequence.

High-level expression of recombinant genes in Escherichia coli is dependent on the availability of the dnaY gene product

We have observed that proteins, such as human tissue-type plasminogen activator, pro-urokinase or gp41 of human immunodeficiency virus, which have a high content of rare codons in their respective genes, are not readily expressed in Escherichia coli. Furthermore induction of these heterologous genes leads to growth inhibition and plasmid instability. Supplementation with tRNA(AGA/AGG(Arg)) by cotransfection with the dnaY gene, which supplies this minor tRNA, resulted in high-level production with greatly improved cell viability and plasmid stability.