The polymerase does not synthesize its transcript at a constant rate A pause rarely lasts longer than 6 milliseconds and might be accompanied by the polymerase moving in reverse along the template
• The polymerase does not synthesize its transcript at a constant rate. • A pause rarely lasts longer than 6 milliseconds and might be accompanied by the polymerase moving in reverse along the template
Termination of a bacterial transcript Transcription is a discontinuous process, with the polymerase pausing regularly and making a choice between continuing elongation or terminating Which choice is depends on which alternative is more favorable in the thermodynamic terms Bacteria appear to use two distinct strategies for transcription termination In the template strand, about half the terminating position contains an inverted palindrome followed by a run of deoxyadenosine nucleotides. Intrinsic terminators Rho dependent
Termination of a bacterial transcript • Transcription is a discontinuous process, with the polymerase pausing regularly and making a “choice” between continuing elongation or terminating. • Which choice is depends on which alternative is more favorable in the thermodynamic terms. • Bacteria appear to use two distinct strategies for transcription termination. • In the template strand, about half the terminating position contains an inverted palindrome followed by a run of deoxyadenosine nucleotides. Intrinsic terminators. • Rho dependent
Template strand DNA EITIT GGCCATCCGC TTTTTGCGGATGGCC TAAAAAAAAAA 5 CCGGTAGGCG CGCCTACCGG ETTTTTTTTTT Transcription RNA5′ FUUUUUUUUUU- 3 c·G A-U base pairs RNA G U·A A·U GGcG G DNA LLLLL RNA polymerase
Rho RNA HH DNA LLLL Elongation complex stalls at a hairpin loop Rho breaks the RNA-DNa base pairs TTTTT
12.1.2 Control over the choice between elongation and termination Antitermination site Promoter Termination signals DNA Antiterminator protein attached to the dna Antiterminator protein (1) HIlT attaches to the RNa polymerase and prevents Termination termination at signal signal 1 number 1
12.1.2 Control over the choice between elongation and termination