EN
E.coli is the most frequently used host-organism for production of heterologous protein from cloned genes.Proper costruction of expression vector is a key factor succesful expression.It should ensure a good segregational stability as well as quarantee induced and regulated gene expression.The most important DNA sequences in he expression vectors are discussed.Gene dosage effect, amplification of recombinant genes, regulation of DNA replication and transcription are described in relation to plasmid stability.