title: Distribution of minigenes in the bacteriophage lambda chromosome.
abstract: The bar loci in the chromosome of bacteriophage lambda inhibit phage vegetative growth in bacteria defective for peptidyl-tRNA hydrolase (Pth). Expression of the bar regions results in accumulation of peptidyl-tRNA, inhibition of protein synthesis, and arrest of mutant cell growth. These effects have been ascribed to the expression of two-codon ORFs present in translatable sequences named 'minigenes' in the lambda bar regions. To investigate the nature, frequency, and distribution of minigenes in the phage genome, we conducted a survey of their location in lambda DNA. A short-fragment random genomic DNA library was constructed for the identification of clones inhibitory of Pth-defective cells (bar-like phenotype). Three new bar-like minigenes were identified in the library but only one was on the sense strand and it had a rare initiation codon. This result contrasted with the in silico identification of over a hundred putative minigenes using an ad hoc computer program on both strands of lambda DNA. Unlike bar constructs, most of the toxic constructed clones were also toxic to wild-type bacteria, thus suggesting a different inhibition mechanism. Sequence analysis of these cloned inserts showed that they harbored minigenes, mini-ORFs, gene starts, gene ends, or combinations thereof. Our data suggest that minigene-like sequences may, at least partly, account for toxicity in wild-type cells. We propose that clustering of minigenes at gene ends may play a role in gene expression. Other minigenes identified in silico were non-toxic. It is still an open question what the in vivo function of these and toxic minigenes might be.
authors.affiliation: Departmento de Genética y Biología Molecular, Centro de Investigación y de Estudios Avanzados del IPN, A.P. 14-740, México DF 07000, Mexico.
authors.forename: Norma-Angélica
authors.initials: NA
authors.lastname: Oviedo
authors.forename: Heladia
authors.initials: H
authors.lastname: Salgado
authors.forename: Julio
authors.initials: J
authors.lastname: Collado-Vides
authors.forename: Gabriel
authors.initials: G
authors.lastname: Guarneros
mesh_terms: D010582:Bacteriophage lambda / Q000235:genetics*; D001483:Base Sequence; D002265:Carboxylic Ester Hydrolases / Q000235:genetics; D002874:Chromosome Mapping / Q000379:methods; D003001:Cloning, Molecular / Q000379:methods; D019295:Computational Biology / Q000379:methods; D004279:DNA, Viral / Q000737:chemistry / Q000235:genetics; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics / Q000821:virology; D023061:Gene Order; D005814:Genes, Viral / Q000235:genetics*; D016679:Genome, Viral; D008969:Molecular Sequence Data; D009154:Mutation; D017422:Sequence Analysis, DNA
chemical_list: D004279:DNA, Viral; D002265:Carboxylic Ester Hydrolases; C019674:aminoacyl-tRNA hydrolase