Successful cloning of an insert into the pGEM®-T or pGEM®-T Easy Vector interrupts the coding sequence of
β-galactosidase; recombinant clones can be identified by color screening on indicator plates. However, the characteristics
of the PCR products cloned into the vectors can significantly affect the ratio of blue:white colonies obtained.
Usually clones containing PCR products produce white colonies, but blue colonies can result from PCR fragments that
are cloned in-frame with the lacZ gene. Such fragments are usually a multiple of 3 base pairs long (including the 3´-A
overhangs) and do not contain in-frame stop codons. There have been reports of DNA fragments up to 2kb that have
been cloned in-frame and have produced blue colonies. Even if your PCR product is not a multiple of 3 bases long, the
amplification process can introduce mutations (deletions or point mutations) that may result in blue colonies.
The Control Insert DNA supplied with the pGEM®-T and pGEM®-T Easy Systems is a 542bp fragment from
pGEM®-luc Vector DNA (Cat.# E1541). This sequence has been mutated to contain multiple stop codons in all six
reading frames, which ensures a low background of blue colonies for the control reaction. Results obtained with the
Control Insert DNA may not be representative of those achieved with your PCR product.