|E.coli under attack from |
Because viruses and phage require host cells to replicate (copy themselves), they are usually simple particles, with their genes (in the form of DNA or RNA) packaged in a shell, often made up of a small number of proteins. In the case of phage lambda (left), around 30-40 genes encode the same number of proteins requiring a total of just under 50 000 base pairs of DNA. The phage head and tail (right) are encoded by the phage. When the phage infects and "sleeps" it enters the genome of the host. When it is awakened, it leaves the host genome and sometimes takes some of the host genetic material with it. This phenomenon is known to occur in animal viruses too and was critical in the isolation of cancer genes, where certain cancers are transmitted by viruses.
Phage lambda is encoded by just under 50 000 base pairs of DNA in a linear chromosome. Last week you used an enzyme called EcoRI to cut the DNA into pieces and then used agarose gel electrophoresis to "visualise" this. Last week's experiment was aimed at ensuring you could carry out the manipulations (microlitre volumes etc) sufficiently accurately for us to carry out the detailed mapping that you can see left. I have posted your data on the Innovation Lab Portal. We have some work to do to get the gels up to scratch, but we will have last week's experience behind us. I shall explain the use of these "molecular scissors", or restriction enzymes in Part II. They will help us map the genes on the phage, with the help of the lambda genome sequence that we can easily access through NCBI.