Phases of growth after infection:

Upon injection of the l genome into E. coli, it circularizes by hybridizing at the cohesive end sites (cos) and DNA ligase seals the circular chromosome.

Transcription begins immediately at the promoters pL and pR. The pL transcript proceeds through gene N with termination of transcription about 80% efficient at tL1. The remainder of the transcript continues to tL2 transcribing the cIII gene where it stops. the pR transcript proceeds through the cro gene where termination at tR1 occurs 50% of the time. The remainder of the transcripts proceed through cII, O, P and terminate at tR2.

This transcription continues until sufficient N protein accumulates whereupon transcription at the above terminators does not occur due to antitermination. Transcription from pL then proceeds through cIII into red, gam, and on into the b region. Transcription from pR now proceeds through tR2 and transcription of the Q gene commences. This transcript terminates before the S and R genes.

When sufficient cro protein builds up it occupies the operators at oR and oL, turning off transcription from these two strong promoters. If sufficient Q protein has accumulated, transcription starting from p'R is antiterminated and it proceeds through the S and R genes and on into the late structural genes, A through J. At this point the cell is committed to the lytic growth phase.

If sufficient cII and cIII protein accumulate, the cII gene product stimulates transcription from two new promoters, pINT and pRE. Transcription from pINT, proceeds through the int gene and from this transcript, integrase required for integration of the circular genome into the E. colichromosome is made. Transcription initiated at pRE proceeds across the antisense strand of the cro gene and into the cI gene. From this transcript, a large burst of the cI repressor is made.

With large amount of the cI repressor formed, the cro repressor is replaced at oR and oL with cI, transcription from pL and pR is quickly repressed and gene expression

of cro, cII, O, P, N and cIII is reduced. By the action of integrase, the genome is integrated into the E. colichromosome.

After all operator sites at oR and oL are occupied, all transcription from the l genome is turned off (what turns off pINT, lack of cII!).

phiEco32

Фаг Т7

Class II promoters (T7 RNAP) (Средние, подавляются лизоцимом gp3.5)

TAATCCG (-10) ACTCACTATA +1 GGGAG A>>

Class III promoters (T7 RNAP) (Поздние) (-17) TAATACAACTCACTAT +1 AAGGAG>>>