Flashcards in Lecture 5+6 - Cloning a Gene/Gene Identification Deck (23)
What is PCR?
Polymerase chain reaction is the amplification of DNA sequences in the lab. PCR requires two primers complimentary to each strand of DNA and a DNA polymerase.
Repetitive heating (denaturing) and cooling (annealing) and DNA synthesis (extension) amplify the DNA between the primer binding sites which yields larger quantities of DNA.
What species can be used as cloning vectors?
Plasmids, Phages (M13, λ), Phagemids, Cosmids, Artificial chromosomes (YACs, PACs, BACs, HACs)
What are YACs?
YAC = Yeast artificial chromosomes
A special linear cloning vector in the form of a yeast artificial chromosome, constructed using chromosomal components including telomeres (from a ciliate), and centromeres, origin of replication, and marker genes from yeast. YACs are used to clone long stretches of eukaryotic DNA.
What is the role of the telomeres in YACs?
The telomeres stabilise the chromosome ends.
How large can the inserts be that are put into YACs?
Very large between 100kb and 10Mb.
What advantages do YACs provide over plasmids as cloning vectors?
Plasmids are relatively small and therefore easy to separate from the host bacterial chromosome and they have relatively few restriction sites. However plasmids can only use bacteria as a host.
YACs (yeast artificial chromosomes) contain telomeres, an origin of replication, and a centromere and are extensively used to clone DNA in yeast. With selectable markers (TRP1 and URA3) and a cluster of restriction sites, DNA inserts ranging from 100 kb to 1000 kb can be cloned and inserted into yeast.
Since yeast, being a eukaryote, undergoes many of the typical RNA and protein processing steps of other, more complex eukaryotes, the advantages are numerous when working with eukaryotic genes.
Plasmids and cosmids suffer from what limitation?
They can only use bacteria as hosts.
What do YACs contain?
A yeast autonomously replicating sequence (ARS)
A yeast centromere (CEN4)
A yeast telomere (TEL)
Genes for YAC selection in yeast (URA3, TRP1)
A supressor tRNA gene (SUP4)
Bacterial replication origin and selectable marker gene
When YACs are cut with EcoRI and BamHI what happens to SUP4?
SUP4 is destroyed and two fragments are created
When SUP4 expressed what colour colonies are produced?
The expression of SUP4 in ade2-ochre mutant yeast suppresses the mutation and results in the formation of WHITE colonies.
PACs are based on what?
PACs are based on P1 bacteriophage.
How many origins of replication do PACs have?
They have two replication origins.
One to control lytic DNA replication (P1 lytic replicon)
One to replicate as a plasmid (P1 plasmid replicon)
In PACs what is pac?
pac is a site cleaved prior to insertion of phage DNA into phage particles.
In PACs what is sacB?
sacB encodes for levansucrase that is toxic for E. coli cells growing on sucrose.
How much DNA can PACs hold?
PACs can hold up to 150kb of DNA
What are PACs cut with?
BamHI and ScaI
How is DNA inserted into PAC vector fragments?
Large genomic DNA is ligated into the BamHI site. The DNA is then packaged in vitro.
Then transfect Cre+ E. coli cells
What are BACs?
BACs are bacterial artificial chromosomes, they are engineered version of F' plasmids
What are the problems arising from the use of BACs?
They produce a low DNA yield.
What are DNA libraries?
DNA libraries are pools of recombinant DNA molecules. They contain fragments of all DNA sequences present in the genome
What are cDNA libraries?
cDNA libraries contain DNA copies of mRNA and are tissue and developmental stage specific. Their formation is dependent on an RNA-dependent DNA polymerase, reverse transcriptase (RT)
List the different cloning vectors by size of DNA insert, largest -> smallest.
Bacteriophage lambda replacement vectors
Bacteriophage lambda insertion vectors
Standard plasmid vector (0-10kb)