Question

What are SOS gene products? How are they induced?

A.

SOS proteins (RecA, SSB, uvrABC, etc); nicked DNA binds to the Lac repressor, causing its release and degradation, thereby triggering expression of the SOS genes

B.

SOS proteins are the heat-shock proteins; the “chi” sequence binds to some transcription factors inducing expression of these genes

C.

SOS proteins are only transcription factors that activate other genes; DNA damage causes induction of these transcription factors through single-stranded DNA binding proteins

D.

SOS proteins (RecA, SSB, uvrABC, etc); ssDNA binds to the repressor Lex A, causing the release and degradation of Lex A, thereby triggering expression of the SOS genes

E.

SOS gene products are micro-RNA molecules that silence the expression of DNA recombination repair proteins; damaged DNA causes induction of these gene products

2. Barbara McClintock first observed the presence of transposable elements in plant genes. Now such “jumping genes” are known to be present in all organisms. This concept is currently used to sequence long unknown DNA sequences by inserting known sequences at random positions inside the unknown sequence. If you were asked to design such a transposon cassette to introduce a known DNA sequence into a long, unknown DNA sequence, what essential sequence elements would you include in the transposon cassette?

A.

The inverted repeats at the two ends, the known DNA sequence, and an antibiotic resistance gene for the selection of genetically altered cells

B.

The transposase gene, the known DNA sequence, and an antibiotic resistance gene for the selection of genetically altered cells

C.

The inverted repeats at the two ends, the transposase gene, the known DNA sequence, and an antibiotic resistance gene for the selection of genetically altered cells

D.

The inverted repeats at the two ends, the transposase gene, and the known DNA sequence

E.

The inverted repeats at the two ends, the transposase gene, a known RNA sequence, a reverse transcriptase gene, and an antibiotic resistance gene for the selection of genetically altered cells

3. You have been asked to express the cystic fibrosis-linked chloride channel selectively in the lung epithelial cells of mice. Since these are dividing cells, to achieve this you use the retroviral technology. The vector containing the chloride channel gene (pRevTRE-chloride channel cDNA) is packaged into live viral particles in a packaging cell line (PT67) and then the viral particles secreted into the medium are injected into mouse lung epithelium. The vector pRevTRE-chloride channel contains the LTR and packaging sequence ψ. Would these injected viral particles replicate in the injected mouse?

A.

No; the packaging cells express proteins that recognize the LTR sequence and promote packaging and replication of the virus

B.

Yes; the ψ sequence is enough for the formation of a viral particle, but the packaging cells contain gene products that stabilize the virus particles

C.

Yes; however, without the packaging cells, the newly formed viral particles are readily lysed in the mouse epithelial cells

D.

No; the packaging cells express the gal, pol, and env proteins that are needed along with the ψ sequence to form the replicating viral particle

Answer 1

Option:- D

Explanation:- SOS proteins (RecA, SSB, uvrABC, etc); ssDNA binds to the repressor Lex A, causing the release and degradation of Lex A, thereby triggering expression of the SOS genes.

Option:- E

Explanation:- The inverted repeats at the two ends, the transposase gene, a known RNA sequence, a reverse transcriptase gene, and an antibiotic resistance gene for the selection of genetically altered cells.