TABLE 1.

L20Δ1 and L20Δ2 repress rpmI expression

Overproduced L20	β-Galactosidase activity (Miller units)	Repression factor
None	102.8
Wild-type	1.67	61.6
L20Δ1	1.37	75.0
L20Δ2	1.17	87.9

The E. coli IBPC5311[λMQ21ΔNB] lysogen, carrying an rpml’-‘lacZ translational fusion, was transformed either with plasmid pBR322 or with plasmid pBL6ec expressing wild-type L20 and its two derivatives pBL6ecΔ6-20 and pBL6ecΔ6-29 expressing the L20Δ1 and L20Δ2 truncations, respectively. pBL6ec is a pBR322 derivative carrying rplT, which is constitutively expressed from a lac promoter and is not subjected to autogenous control. The repression factor is defined as the ratio of the β-galactosidase activity assayed in the presence of control plasmid pBR322 to the activity assayed in the presence of wild-type L20- or truncated L20-overproducing plasmid.