Duplex (or quadruplet) CH domain containing human multidomain proteins: an inventory.

In this paper, the inventory presented for singlet CH (calponin homology/actin binding) domain containing human multidomain proteins is extended to several duplex and one quadruplet CH containing forms. Invariably, the duplexes are located at the begin of the molecules. The regions connecting the two CH units suggest amino acid conservations which allows the placing of 18 duplex containing molecules into six groups wherein the gene for one member in each group created the others more recently by gene duplication. The ancient multidomain proteins, possibly, were primarily the result of an exon shuffling (transposition) mechanism that also guided the placing of the CH singlet or duplex domain at the amino end of the newly created proteins. A mechanism that creates pseudogenes could conceivably produce genes that encode multi-domain proteins. Intragenomic duplications (slippage) might have facilitated the occurrence of encoding repeats, thus allowing for the creation of multiple identical domains within one molecule. Gene duplication with subsequent modification and small domain gene recombination which formed multidomain proteins are important forces driving evolution.