A new option for chemical labelling of oligonucleotide probes with biotin molecules.

Utilization of molecular probes for identification of pathogenic microorganisms have great advantages if we compare results obtained with classic systems traditionally employed in the clinic and research laboratories. This new method with biotin is more sensitive and specific than others and exclude the use of radioactive markers.

Transcription of a bacteriophage lambda DNA site blocks growth of Escherichia coli.

The rap mutation in Escherichia coli prevents the growth of bacteriophage lambda. Phage mutations that overcome rap inhibition (bar) have been mapped to loci in the pL operon. We cloned and sequenced three mutations in two of these loci: barIa to the left arm of the lambda attachment site (attP) and barII in the ssb (ea10) gene. The mutations represent single base-pair changes within nearly identical 16-base-pair DNA segments. Each mutation disrupts a sequence of dyad symmetry within the segment. Plasmids carrying a bar+ sequence downstream to an active promoter are lethal to rap, but not rap+, bacteria. The bar sequences isolated from the lambda bar mutants are not lethal. We synthesized a minimal lambda barIa+ sequence, 5'-TATATTGATATTTATATCATT, and cloned it downstream to an inducible promoter. When transcribed, this sequence is sufficient to kill a rap strain.