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The use of general descriptive names, registered names, trademarks, etc. in this publication does not imply, even in the absenee of a specific statement, that such names are exempt from the relevant proteetive laws and regulations and therefore free for general use.

SummaryBacterial cytokinesis requires the divisome, a complex of proteins that co-ordinates the invagination of the cytoplasmic membrane, inward growth of the peptidoglycan layer and the outer membrane. Assembly of the cell division proteins is tightly regulated and the order of appearance at the future division site is well organized. FtsQ is a highly conserved component of the divisome among bacteria that have a cell wall, where it plays a central role in the assembly of early and late cell division proteins. Here, we describe the crystal structure of the major, periplasmic domain of FtsQ from Escherichia coli and Yersinia enterocolitica. The crystal structure reveals two domains; the a-domain has a striking similarity to polypeptide transport-associated (POTRA) domains and the C-terminal b-domain forms an extended b-sheet overlaid by two, slightly curved a-helices. Mutagenesis experiments demonstrate that two functions of FtsQ, localization and recruitment, occur in two separate domains. Proteins that localize FtsQ need the second b-strand of the POTRA domain and those that are recruited by FtsQ, like FtsL/FtsB, require the surface formed by the tip of the last a-helix and the two C-terminal b-strands. Both domains act together to accomplish the role of FtsQ in linking upstream and downstream cell division proteins within the divisome.

The use of general descriptive names, registered names, trademarks, etc. in this publication does not imply, even in the absenee of a specific statement, that such names are exempt from the relevant proteetive laws and regulations and therefore free for general use.

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Growth of diameter of individual trees can be expressed as diameter increment or basal area increment. Little work has been done to determine which of these parameters is preferable for use in growth studies. This paper examines growth of trees in pure and mixed stands of even-aged, regrowth forest of Eucalyptusregnans, E. obliqua, and E. globulus, aged 6-80 years, thinned and unthinned, in southeastern Tasmania. Weighted least squares regression equations are developed to relate diameter and basal area increments, over 1- to 6-year increment periods, to initial tree diameter in 29 growth plots. The correlation between basal area increment and initial diameter was always greater than that between diameter increment and initial diameter in these relationships. Despite this, the precision of estimates of future diameter in each plot is shown to be the same whether diameter or basal area increment equations are used. Data from a thinning experiment in 38- to 85-year-old, even-aged Acersaccharum, Fraxinusamericana, and Prunusserotina stands in southern Ontario are also examined and similar results obtained. It is concluded that no apriori reason exists for expressing growth as diameter increment or basal area increment in studies of these types.