Cloning in Bacteria and Eukaryotes
Cloning in bacteria
Bacteria can be classified into (i) gram negative bacteria e.g. Escherichia coli. Pseudomonas, Rhizobium and (ii) gram positive bacteria e.g. Bacillus subtilis and Streptomycetes sp. Ordinarily plasmids can not maintain themselves in stable form in both classes of bacteria and, therefore, plasmid vector for two classes usually differ. While for gram negative bacteria, plasmids, phages and cosmids are known as vectors, for gram positive bacteria, only plasmids are known to do this job.
Cloning in eukaryotes
Since chromosomes found in the nucleus in eukaryotes are separated from the rest of cell through nuclear membrane, and since many of the genes are split genes with exons and introns, genetic engineering with eukaryotes requires new methods and tools. When eukaryotic genes are cloned in prokaryotes, the split genes can not be correctly expressed, because prokaryotes do not have the equipment necessary for splicing out the RNA transcribed from the introns of a gene.