Strategies to Study Distribution and Function of Minigenes in Microorganisms

The genomes of bacteria and their viruses harbor nucleotide sequences that encode very short peptides. Although these small "genes," named minigenes, have been dismissed as genomic curiosities, we have shown that they are functionally recognizable. Minigenes are transcribed into messenger molecules, or mRNAs, which are translated on ribosomes, the cellular organelles where the synthesis takes place. However, contrary to most messengers which are translated into mature proteins, some minigene mRNAs provoke peptidyl-tRNA release at high frequency. Under limiting peptidyl-tRNA hydrolase activity, tRNA remains sequestered and translation stops. Most of the above conclusions have been derived from minigene overexpression. It is possible that the role of minigenes in the cell may be more complex than just to inhibit protein synthesis. Nevertheless, fewer than expected lethal minigenes were found in a survey of a random library constructed from lambda DNA small fragments. Lethality by over expression of foreign genes, usually rich in rare codons, is common in E. coli. We think that at least some of those events may be explained by an inhibition mechanism similar to that of minigenes.