The acceptor vectors pAX and pKOIX. Structure of pKOIX and pAX acceptor plasmids. The loxprom site that consists of a loxP site (green) and the bacterial promoter (yellow) was inserted into pH4T2 by using the NotI and EcoRI and into pKOI by EcoRI restriction sites, respectively. The arrow head in the loxP sites indicates the loxP orientation. The gray/black parts correspond to the backbone sequences that are necessary for propagation in E. coli, and the red part of both acceptor vectors illustrate the neo2 selection cassette for selection in T. thermophila by paromomycin. The purple colored part of pAX illustrates the AT-rich double rDNA ori which is necessary for the propagation in T. thermophila. The blue part in pKOIX shows the AT-rich 5' and 3' integration sequences (bright blue, up/downstream and dark blue coding sequences). They are part of the endogenous DHFR-TS gene locus.(Bottom: detail of loxprom site).