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Cluster-randomized trials, in which health interventions are allocated randomly to intact clusters or communities rather than to individual subjects, are increasingly being used to evaluate disease control strategies both in industrialized and in developing countries. Sample size computations for such trials need to take into account between-cluster variation, but field epidemiologists find it difficult to obtain simple guidance on such procedures.

The mammalian beta-like globin gene family has served as an important model system for analysis of tissue- and developmental state-specific gene regulation. Although the activities of a number of regulatory proteins have been implicated in the erythroid cell-specific transcription of globin genes, the mechanisms that restrict their expression to discrete stages of development are less well understood. We have previously identified a novel regulatory element (PRE II) upstream from the human embryonic beta-like globin gene (epsilon) that synergizes with other sequences to confer tissue- and stage-specific expression on a minimal epsilon-globin gene promoter in cultured embryonic erythroid cells. Binding of an erythroid nuclear protein (PRE II-binding factor [PRE-IIBF]) to the PRE II control element is required for promoter activation. Here we report on some of the biochemical properties of PREIIBF, including the characterization of its specificity and affinity for DNA. The embryonic and adult forms of PREIIBF recognize their cognate sequences with identical specificities, supporting our earlier conclusion that they are very similar proteins. PREIIBF binds DNA as a single polypeptide with an Mr of approximately 80,000 to 85,000 and introduces a bend into the target DNA molecule. These results suggest a mechanism by which PREIIBF may contribute to the regulation of the embryonic beta-like globin gene within the context of a complex locus.

Although malaria is known to be a major cause of child mortality and morbidity throughout sub-Saharan Africa there are few detailed studies of malaria mortality rates and incidence of severe malarial disease in defined communities. We have studied the geographical pattern of admissions to hospital with severe malaria and the stability of this pattern over time in Kilifi District on the Kenyan Coast.

Unprotected heterosexual contact in the presence of other sexually transmitted diseases (STD) enhances the probability of HIV transmission. The objective of this study was to estimate the proportion of HIV infections attributable to STD in rural Uganda.

The use of plant DNA viruses as vectors for the transfer of foreign genes to plants offers two potential advantages over other, existing methods of producing transgenic plants. First, these viruses sys-temically infect whole plants, thus obviating the need for the difficult and time-consuming step of regeneration from transformed single cells or protoplasts. Second, the viruses replicate as separate, autonomous entities within the plant's cells so that any gene cloned in a plant DNA-virus vector would be amplified to high copy number, a feature that differs from methods that produce transgenic plants by the chromosomal integration of foreign DNA. To date, attention has focused on the development of vectors based on the cauliflower mosaic virus (CaMV), but their use is hampered by the narrow range of plants infected by CaMV, and by practical limitations on inserting foreign DNA that are imposed by the biology of CaMV. Here we describe the use of vectors based on the gemini tomato golden mosaic virus (TGMV) to introduce the neomycin phosphotransferase (neo gene) into plants. Our results indicate that geminivirus-derived vectors should be useful not only for amplification of gene expression by the systemic infection of plants, but also for heritable gene amplification by the integration of stable master copies of the vector into the plant chromosomal DNA.