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C R Calladine

Publications and source records attributed to C R Calladine.

26 records · Page 2Linked to original sources
PubMed1984

A base-centred explanation of the B-to-A transition in DNA.

In the traditional view, the bistable feature responsible for the switch between the B and A forms of DNA was the sugar-phosphate backbone. Several recent assays of the sequence-dependent structure of DNA are not compatible with that hypothesis. Here we show that certain kinds of base-pair step, mainly those of the pyrimidine-purine variety, can stack in a "bistable" fashion so as to produce one of two overall helix shapes A or B. Further, we suggest that the passive, elastic stiffness of the backbone is responsible for communicating the stacking configuration from bistable steps to their "neutral" neighbours. The role of water molecules, in stabilizing the B form of DNA over the A, may simply be to form hydrogen-bonded bridges with the minor-groove edges of neutral steps in the B configuration.

Base Sequence↗
PubMed1982

Construction of bacterial flagellar filaments, and aspects of their conversion to different helical forms.

The helical flagellar filaments of bacteria such as Salmonella typhimurium are constructed from subunits of a single protein called flagellin by a process of self-assembly. They are polymorphic, and change from one helical form to another in a variety of circumstances. This paper discusses, from a viewpoint of classical mechanics, two types of problem associated with these filaments. First is the general problem of how to construct a helical rod from identical subunits. There must be some variation in the pattern of packing of subunits; and it is demonstrated that a mechanically bi-stable but otherwise linear-elastic subunit can build filaments which are not only helical but also possess the observed polymorphic properties. The question of uniqueness of the design is discussed. The second problem concerns the hydrodynamic performance of a helical filament which can switch waveform when subjected to mechanical overload. Transitions which can be brought about in this way are reviewed briefly. An explanation is offered in terms of the mechanics of polymorphism for the behaviour of an anomalous and puzzling 'partly rotating' filament in Hotani's (1979) micro-video study of tethered filaments in fluid streams.

Bacteria↗