Genetic redundancy means that two or more genes are performing the same function and that inactivation of one of these genes has little or no effect on the biological phenotype

Redundancy seems to be widespread in genomes of higher organisms

TLS Online TPP Program

#Id: 6756

#Unit 3. Fundamental Processes

Method for determining mRNA half-lives.

RNA polymerase II transcription is shut down, either by a drug or a temperature shift in strains with a temperature sensitive mutation in a Pol II gene. The levels of specific mRNAs are determined by northern blot or RT-PCR at various times following shutdown.

TLS Online TPP Program

#Id: 6757

#Unit 3. Fundamental Processes

In E. coli the typical mRNA half-life is about 3 minutes, but half-lives of individual mRNAs may be as short as 20 seconds or as long as 90 minutes.  In budding yeast, mRNA half-lives range from 3 to 100 minutes, whereas in metazoans, half-lives range from minutes to hours, and in rare cases, even days.

TLS Online TPP Program

#Id: 6758

#Unit 3. Fundamental Processes

Degradation of bacterial mRNAs is initiated by removal of a pyrophosphate from the 5’ terminus. The monophosphorylated form stimulates the catalytic activity of an endonuclease RNase E

TLS Online TPP Program

#Id: 6759

#Unit 3. Fundamental Processes

PNPase a 3’ to 5’ exonucleases in E. coli, are unable to progress through double-stranded regions. Thus, the stem-loop structure at the 3’ end of many bacterial mRNAs protects the mRNA from direct 3’ attack.

TLS Online TPP Program

#Id: 6760

#Unit 3. Fundamental Processes

RNase E and PNPase, along with a helicase and another accessory enzyme, form a multiprotein complex called the degradosome.

TLS Online TPP Program

#Id: 6761

#Unit 3. Fundamental Processes

Cytoplasmic mRNAs are degraded by one of the three pathways. For most mRNAs, the deadenylation-dependent pathway is followed These dense regions of cytoplasm contain the decapping enzyme (DCP1/DCP2), activators of decapping (DHH, PAT1, LSM1-7), and the major 5′→3′ exoribonuclease XRN1, as well as densely associated mRNAs