bioreactor studies of heterologous protein production by ...

1- fkquently than a plasmid with Iowa copy number. However, opposing results have
been observed. For example, the 2 piasrnid is more stable than either YEp plasmid or
YRp plasmid even though the latter is usoaliy present in higher copy auraber (Spalding
and Tuite, 1989). Spalding and Tuite (1989) mer nported that the stability of the YRp
piasmid (YRp7M) in a haploid strain was significantly less than that of the YEp plasmid
(pMMa), although the former had an approximately sever6old higher copy number. ?bis
apparent inconsistency occurs because YRp plasmids have no effective plasmid-encoded
partition systern, and show a suong segregation bias toward the mother œil during mitotic
division (Spalding and Tuite. 1989). Thus, a plasmid with high copy number does not
necessarüy guamntee its stability unless it has an effective partitionhg system. The lam
depends on the efficiency of the ongin of replication. Effeaive on regions were found to
consist of two fundamental domains: a replicatiofiinducing sequence, and a repiication-
enhancer sequence. The enhancer sequence is not essentiai, but ensures optimal stabüity
of the ori-containing vector (Montiel et al., 1984). The efnciency of 2 prn origin is higher
than that of ARSI ongin (Spaiiding et ai, 1989), as was cohed also by Da Silva and
BaiIey (1991). The cloned gene product's synthesis was much lower with the ARSI
plasmid than that with the 2 pm-based phsrnid because of the malier M o n of plasmid-
bearing ceh (7.5%) when the phsrnid's origin of replication was the ARSI element @a
Silva and Baüey, 1991). Increased stability with hcreased copy nurnber has been reported
for 2 j.im based plasmids (Caunt et ai., 1988). Qewiy, the efkct of copy number on
plasmid staùility reIates to the origins of replication. Stability depends on efficiency of the