------------------------------------------------------------- Bases Functions ------------------------------------------------------------- 142- 147 Promoter for beta-gal (-30 signal), induced by IPTG 176- 180 Promoter for beta-gal (-10 signal) 216- 539 beta-galactosidase codons 230- 289 mcs (polylinker) 885-1745 beta-lactamase codons -------------------------------------------------------------The above is a summary of the sites on pUC19 based on information gathered from related parent files, e.g., M13mp19, pBR322, beta-galactosidase, etc. The plasmid is a mix-and-match of features taken from various parents. The pUC19's mcs (multiple cloning site), which is also called polylinker, resides within the beta-galactosidase codons. It is a fairly small region that is recognized by many restriction enzymes. This is normally the insertion point for foreign genes.
pUC19 has genes for two enzymes: beta-galactosidase and beta-lactamase. The expression of beta-galactosidase is under the control of the lac promoter, which is induced by IPTG. Beta-galactosidase is an enzyme that digests galactose. X-gal is a specially treated chromogenic galactose analog that releases a blue color when acted upon by beta-galactosidase. Galactose is normally not required for cell growth. Thus, beta-galactosidase is an integral part of a color indicator for screening and selection. Colonies of cells contaning plasmids with intact beta-galactosidase appear blue in the presence of X-gal/IPTG, while those of cells lacking an intact beta-galactosidase gene appear white.
Beta-lactamase breaks down ampicillin (an antibiotic) and renders the antibiotic harmless to the host. This, too, is useful for screening and selection. Cells containing plasmids with intact beta-lactamase gene can grow in ampicillin to form colonies, while those lacking an intact beta-lactamase gene cannot grow in ampicillin.
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