Question

and hydrolase gone (ORF2, treft) for the utilization of 4. (13 pts) Below is an E.coli operon encoding a transporter gene (ORF1. tre a non-glucose sugar trehalose. The coding strand is shown here. Start of ORF1 End of ORF2 tret treh

Answer 1

1. SD sequence:

• Ribosome binding site (RBS) is nucleotide sequence present upstream (2 or 3 to 7 or10 nucleotides upstream) of start codon (AUG) in mRNA. This sequence is important (though not absolute essential) for initiation of translation in prokaryotes (like bacteria).
• This sequence, also referred to as Shine-Dalgarno’s (SD) sequence, comprises of 5’ untranslated region (UTR) in mRNA and is purine rich. A complementary pyrimidine rich 3’ sequence (anti-SD sequence) is present in the 16S rRNA of ribosomal subunit. This interaction between the SD sequence of rRNA and anti-SD sequence of mRNA plays an important role (in most cases) for initiation of translation in prokaryotes.

2. Operator:

• Operon comprises of different types of gene:
• Structural genes b. Controlling genes- promoter/ operator.
• All genes under the same promoter/ operator system are expressed at the same time together (on and off together).
• Operator is the region where the repressor binds.

3. Terminator:

• Transcription is terminated at the terminator sequence.
• Terminator sequence signals the dettachment of the RNA polymerase.

4.

• Transcription termination may be Rho dependent or Rho independent.
• In Rho dependent termination: Rho protein binds to the terminator sequence without secondary structure, hair- pin structures further formed to halt RNA polymerase.
• In Rho independent termination: the terminator sequence have series of adenine (A) or poly U (or) on RNA, along with inverted repeats, forming hair-pin structures.
• Thus the presence of inverted repeats with T indicates Rho independent termination.