This set of Advanced Vector Biology Questions and Answers focuses on “Vectors and Cloning in Gram – Positive Bacteria – 3”.
1. The promoters of B. subtilis vectors have conserved polyA and ________ tails.
a) PolyT
b) PolyC
c) PolyG
d) PolyA
View Answer
Explanation: The promoters also have conserved polyA and polyT tracts upstream of the -35 region. Some promoters also have a -16 region.
2. Ribosomes from _________ recognize only homologous mRNA.
a) E. coli
b) B. subtilis
c) Yeast
d) Bacteriocins
View Answer
Explanation: E. coli ribosomes can support protein synthesis when directed by mRNA from a range of Gram-positive and Gram-negative organisms, whereas Ribosomes from B. subtilis recognize only homologous mRNA.
3. The selectivity of ribosomes of B. subtilis is due to the lack of ________
a) Inducer
b) Promoter
c) Protein S1
d) Repressor
View Answer
Explanation: Ribosomes from B. subtilis recognize only homologous MRNA. This is because they lack a counterpart of the largest E. coli Ribosomal protein.
4. Which of the following does not lack MRNA selectivity?
a) Streptococcus
b) Clostridium
c) E. coli
d) Lactobacillus
View Answer
Explanation: Few gram-positive bacteria such as staphylococcus, streptococcus, clostridium, and lactobacillus, lack S1-equivalent E.coli protein and therefore exhibit MRNA selectivity.
5. The role of S1 is to bind ________ non-specifically.
a) MRNA
b) RNA
c) DNA
d) CDNA
View Answer
Explanation: The role of S1 is to bind RNA non-specifically and bring it to the decoding site of the 30S subunit, where proper positioning of the Shine-Dalgarno sequence and initiation codon signals can take place.
6. When was the Spac system for low-GC hosts developed?
a) 1990
b) 1984
c) 1963
d) 1936
View Answer
Explanation: The first controlled expression system to be used in B. subtilis was the Spac system, developed by Yansura and Henner in 1984.
7. Which gene of E. coli is contained in the Spac system?
a) Tol
b) Amp
c) LacI
d) Gal
View Answer
Explanation: The first controlled expression system to be used in B. subtilis was the Spac system. This consists of the E. coli lacI gene and the promoter of phage SPO-1.
8. A promoter from which phage is incorporated in the Spac system?
a) Lambda
b) M13
c) Prophage
d) SPO-1
View Answer
Explanation: The first controlled expression system to be used in B. subtilis was the Spac system. This consists of the E. coli lacI gene and the promoter of phage SPO-1.
9. E. coli T7 system is successfully implemented in B. subtilis.
a) True
b) False
View Answer
Explanation: E. coli T7 system is implemented in B. subtilis by inserting the T7 RNA polymerase gene into the chromosome under the control of the Xylose-inducible promoter and cloning the gene of interest, coupled to T7 promoter, on a B. subtilis vector.
10. The promoter used in T7 system is inducible by which of the following?
a) Xylose
b) Galactose
c) Lactose
d) Fructose
View Answer
Explanation: E. coli T7 system is implemented in B. subtilis by inserting the T7 RNA polymerase gene into the chromosome under the control of the Xylose-inducible promoter and cloning the gene of interest, coupled to T7 promoter, on a B. subtilis vector.
11. Expression of a heterologous gene in the T7 system is ____________
a) Easy
b) Difficult
c) Not possible
d) Costly
View Answer
Explanation: Expression of a heterologous gene in the T7 expression system can be made simpler by putting it directly under the control of the promoter.
12. Other than B. subtilis, the T7 expression system can also be used in __________
a) Lactobacillus
b) Yeast
c) Fungi
d) Agrobacterium
View Answer
Explanation: A xylose inducible system has also been developed in lactobacillus and staphylococci. Many different controllable promoters are available.
13. In the phi-31 system of L. lactis, _________ vector is used.
a) Hybrid
b) Mammalian
c) Low copy number
d) High copy number
View Answer
Explanation: In the phi-31 system of L. lactis, the gene of interest is placed under the control of a phage middle promoter inserted in a low copy number vector carrying the phage region ori.
14. In the phi-31 system of L. lactis, gene of interest is placed under the control of _____________ promoter.
a) Weak
b) Strong
c) End
d) Middle
View Answer
Explanation: In the phi-31 system of L. lactis, the gene of interest is placed under the control of a phage middle promoter inserted in a low copy number vector carrying the phage region ori.
15. Following infection with phi-31, __________ increases.
a) Copy number
b) Mortality rate
c) Size
d) Protein production
View Answer
Explanation: Following infection of the host cell with phi-31, the plasmid copy number rapidly increases and this is followed by expression from the phage promoter.
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