enzymatically synthesized from the sequences present in an mrna template transformation the process of stably and heritably altering the genotype of a recipient cell microorganism by the introduction of purified dna this is typically detected by a change in the phenotype of the recipient organism transcription the process of producing mrna template from a structural gene expression the process starting with a structural gene of producing its polypeptide being a combination of transcription and translation an expression vector is a plasmid derived construction designed to enable the expression of a gene carried on the vector plasmid an extrachromosomal double stranded dna sequence comprising an intact 34 replicon 34 such that the plasmid is replicated in a host cell when the plasmid is placed within a unicellular organism the characteristics of that organism may be changed or transformed as a result of the expression of the dna sequences of the plasmid for example a plasmid carrying the gene for tetracycline resistance transforms a cell previously sensitive to tetracycline into one which is resistant to it expression vector includes vectors which are capable of expressing dna sequences contained therein where such sequences are operably linked to other sequences capable of effecting their expression such as promoter sequences it is implied although not always explicitly stated that these expression vectors must be replicable in the host organism either as episomes or as an integral part of the chromosomal dna clearly a lack of replicability would render the expression vectors effectively inoperable a functional definition of an expression vector is any dna.