Antigenic variation in African trypanosomes is induced by DNA double-strand breaks (DSBs). In these protozoan parasites, DSB repair (DSBR) is dominated by homologous recombination (HR) and microhomology-mediated end joining (MMEJ), while non-homologous end joining (NHEJ) has not been reported. To facilitate the analysis of chromosomal end-joining, we established a system whereby inter-allelic repair by HR is lethal due to loss of an essential gene. Analysis of intrachromosomal end joining in individual DSBR survivors exclusively revealed MMEJ-based deletions but no NHEJ. A survey of microhomologies typically revealed sequences of between 5 and 20 bp in length with several mismatches tolerated in longer stretches. Mean deletions were of 54 bp on the side closest to the break and 284 bp in total. Break proximity, microhomology length and GC-content all favored repair and the pattern of MMEJ described above was similar at several different loci across the genome. We also identified interchromosomal gene conversion involving HR and MMEJ at different ends of a duplicated sequence. While MMEJ-based deletions were RAD51-independent, one-sided MMEJ was RAD51 dependent. Thus, we describe the features of MMEJ in Trypanosoma brucei, which is analogous to micro single-strand annealing; and RAD51 dependent, one-sided MMEJ. We discuss the contribution of MMEJ pathways to genome evolution, subtelomere recombination and antigenic variation.

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Bismuth vanadate (BiVO4) is a promising photoanode material; however, its efficiency significantly changes depending on the atomic ratio of Bi/V, and there is no suitable method for synthesizing large-area photoanodes. In this study, an efficient BiVO4 photoanode was fabricated via sputtering, by manipulating the molar ratio of Bi/V with V solution annealing. V solution annealing not only adjusted the atomic ratio of Bi/V but also increased the number of O vacancies, thereby improving the charge-separation and charge-transport efficiencies. Consequently, the photocurrent density of the sputtered photoanode with V solution annealing (BVO-V) was 1.86 mA/cm2, which is 23 times higher than that of the sputtered photoanode annealed under air conditions (BVO-A, 81.0 μA/cm2). Furthermore, microcone-patterned fluorine-doped SnO2 was fabricated to increase the active area and reduce the high reflectance, owing to the dense deposition because of the sputtering. Thus, the photocurrent density of the MC-BVO was 3.11 mA/cm2, which is approximately 67% higher than that of BVO-V (1.86 mA/cm2).

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