Question

The solution of situational problems.

RNA polymerase recognition site -5’ TATATT 3’, -35 nucleotide sequence – 5’ TTGACA 3’

The site of recognition of the repressor protein in the operon (operator) is ATTTTAT, structural genes begin with TAC codons and end with ATC codons, TTTT spacer sites are located between the genes.

a) Using this data, construct a Lac-operon model consisting of three structural genes: the Z- structural gene consists of 5 codons, the Y and A structural genes are 4 codons.

b) Perform a transcription. How much RNA is formed from this site?

c) How many proteins are encoded in this DNA region? Define their structure.

Answer 1

RNA polymerase recognition site -5’ TATATT 3’, -35 nucleotide sequence – 5’ TTGACA 3’

The site of recognition of the repressor protein in the operon (operator) is ATTTTAT, structural genes begin with TAC codons and end with ATC codons, TTTT spacer sites are located between the genes.

a) Using this data, construct a Lac-operon model consisting of three structural genes: the Z- structural gene consists of 5 codons, the Y and A structural genes are 4 codons.

b) Perform a transcription. How much RNA is formed from this site?

c) How many proteins are encoded in this DNA region? Define their structure.

Answer:

Lac-operon model:

| promoter | operator | | | | | | |

5’-TTGACA-___-TATATT-___-ATTTTAT-___-TTTT-TAC-___-ATC-TTTT-TAC-___-ATC-TTTT-TAC-___-ATC-3’

-35 some -10 recognition lacZ lacY lacA

seq. site of ope-

rator

Only one messenger RNA is formed from this site.

There are 3 proteins that are incoded in this DNA region: β-galactosidase (lacZ),  β-galactoside permease (lacY), β-galactoside transacetylase (lacA).