Restriction-modification gene complexes as selfish gene entities: Roles of a regulatory system in their establishment, maintenance, and apoptotic mutual exclusion

We have reported some type II restriction-modification (RM) gene complexes on plasmids resist displacement by an incompatible plasmid through postsegregational host killing. Such selfish behavior may have contributed to the spread and maintenance of RM systems. Here we analyze the role of regulatory genes (C), often found linked to RM gene complexes, in their interaction with the host and the other RM gene complexes. We identified the C gene of EcoRV as a positive regulator of restriction. A C mutation eliminated postsegregational killing by EcoRV. The C system has been proposed to allow establishment of RM systems in new hosts by delaying the appearance of restriction activity. Consistent with this proposal, bacteria preexpressing ecoRVC were transformed at a reduced efficiency by plasmids carrying the EcoRV RM gene complex. Cells carrying the BamHI RM gene complex were transformed at a reduced efficiency by a plasmid carrying a PvuII RM gene complex, which shares the same C specificity. The reduction most likely was caused by chromosome cleavage at unmodified PvuII sites by prematurely expressed PvuII restriction enzyme. Therefore, association of the C genes of the same specificity with RM gene complexes of different sequence specificities can confer on a resident RM gene complex the capacity to abort establishment of a second, incoming RM gene complex. This phenomenon, termed “apoptotic mutual exclusion,” is reminiscent of suicidal defense against virus infection programmed by other selfish elements. pvuIIC and bamHIC genes define one incompatibility group of exclusion whereas ecoRVC gene defines another.

Chromophore-bearing NH2-terminal domains of phytochromes A and B determine their photosensory specificity and differential light lability.

In early seedling development, far-red-light-induced deetiolation is mediated primarily by phytochrome A (phyA), whereas red-light-induced deetiolation is mediated primarily by phytochrome B (phyB). To map the molecular determinants responsible for this photosensory specificity, we tested the activities of two reciprocal phyA/phyB chimeras in diagnostic light regimes using overexpression in transgenic Arabidopsis. Although previous data have shown that the NH2-terminal halves of phyA and phyB each separately lack normal activity, fusion of the NH2-terminal half of phyA to the COOH-terminal half of phyB (phyAB) and the reciprocal fusion (phyBA) resulted in biologically active phytochromes. The behavior of these two chimeras in red and far-red light indicates: (i) that the NH2-terminal halves of phyA and phyB determine their respective photosensory specificities; (ii) that the COOH-terminal halves of the two photoreceptors are necessary for regulatory activity but are reciprocally inter-changeable and thus carry functionally equivalent determinants; and (iii) that the NH2-terminal halves of phyA and phyB carry determinants that direct the differential light lability of the two molecules. The present findings suggest that the contrasting photosensory information gathered by phyA and phyB through their NH2-terminal halves may be transduced to downstream signaling components through a common biochemical mechanism involving the regulatory activity of the COOH-terminal domains of the photoreceptors.

American waterfowl; their present situation and the outlook for their future,

Each plate accompanied by guard sheet with descriptive letterpress.

Cattle ... being a treatise on their breeds, management, and diseases ... /

Mode of access: Internet.

Report of the Committee on a Treatise on Marine Ecology and Paleoecology, 1946-1947 /

"Presented in preliminary form as Appendix H at the Annual Meeting of the Division, May 2, 1947."

Sanderson's duettinos, or, Select violin miscellany : comprising a series of the most esteemed songs, airs, marches, waltzes, quadrilles, &c arranged in their proper keys as duetts for two violins /

Mode of access: Internet.

Metropolitan borough councils, their constitution, powers and duties.

Mode of access: Internet.

Borough councils : their constitution, powers and duties /

Mode of access: Internet.

The poor laws : their present operation, and their proposed amendment /

Mode of access: Internet.

A compleat treatise of the gravel and stone : wherein all their symptoms, causes and cures, are mechanically accounted for ... /

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Agricultural counties : their location, farms and economies /

"February 1981."

A manual of modern history : containing the rise and progress of the principal European nations, their political history, and the changes in their social condition, with a history of the colonies founded by Europeans /

Mode of access: Internet.

DCPA national directory of fallout shelter analysts and their associated architectural and engineering firm.

Chiefly tables.

A hand-book to the flora of Ceylon, containing descriptions of all the species of flowering plants indigenous to the island, and notes on their history, distribution, and uses.

Parts IV-V continued by Sir J.D. Hooker.

Standard perfection poultry book; the recognized standard work on poultry, turkeys, ducks and geese, containing a complete description of all the varieties, with instructions as to their diseases, breeding and care. Incubators, brooders, etc. for the farmer, fancier, or amateur,

Mode of access: Internet.