BS-RNASE TETRAMERS - AN EXAMPLE OF DOMAIN-SWAPPED OLIGOMERS

In the ribonuclease superfamily, dimericity is a unique feature of bov ine seminal RNase (BS-RNase). In about two-thirds of native BS-RNase m olecules, the two subunits interchange their N-terminal tails, thus ge nerating domain-swapped dimers (MxM), which mostly responsible for enz yme biological activities and allostericity. Higher molecular weight B S-RNase oligomers can also be prepared [Libonati, M. (1969) Ital. J. B iochem. 18, 407-417.]. This paper reports on BS-RNase tetrameric deriv atives which were isolated and enzymatically characterized. The data c ollected and the analysis of the crystal packing of MxM dimers suggest ed a structural model for tetramer assembly, in which the four subunit s are enchained by multiple domain-swapping events.