Glucose-6-phosphate dehydrogenase (G6PD) deficiency, the most common enzymopathy of humans, affects over 400 million people. The geographical correlation of its distribution with the historical endemicity of malaria suggests that this disorder has risen in frequency through natural selection by malaria. However, attempts to confirm that G6PD deficiency is protective in case-control studies of malaria have yielded conflicting results. Hence, for this X-linked disorder, it is unclear whether both male hemizygotes and female heterozygotes are protected or, as frequently suggested, only females. Furthermore, how much protection may be afforded is unknown. Here we report that, in two large case-control studies of over 2,000 African children, the common African form of G6PD deficiency (G6PD A-) is associated with a 46-58% reduction in risk of severe malaria for both female heterozygotes and male hemizygotes. A mathematical model incorporating the measured selective advantage against malaria suggests that a counterbalancing selective disadvantage, associated with this enzyme deficiency, has retarded its rise in frequency in malaria-endemic regions. Although G6PD deficiency is now regarded as a generally benign disorder, in earlier environmental conditions it could have been significantly disadvantageous.

b TFIIB-related factor Brf1 is essential for RNA polymerase (Pol) III recruitment and open-promoter formation in transcription initiation. We site specifically incorporated a nonnatural amino acid cross-linker into Brf1 to map its protein interaction targets in the preinitiation complex (PIC). Our cross-linking analysis in the N-terminal domain of Brf1 indicated a pattern of multiple protein interactions reminiscent of TFIIB in the Pol active-site cleft. In addition to the TFIIB-like protein interactions, the Brf1 cyclin repeat subdomain is in contact with the Pol III-specific C34 subunit. With site-directed hydroxyl radical probing, we further revealed the binding between Brf1 cyclin repeats and the highly conserved region connecting C34 winged-helix domains 2 and 3. In contrast to the N-terminal domain of Brf1, the C-terminal domain contains extensive binding sites for TBP and Bdp1 to hold together the TFIIIB complex on the promoter. Overall, the domain architecture of the PIC derived from our cross-linking data explains how individual structural subdomains of Brf1 integrate the protein network from the Pol III active center to the promoter for transcription initiation. Eukaryotic RNA polymerase (Pol) III transcribes precursor tRNAs, 5S rRNA, small nuclear RNAs such as U6 and 7SK RNAs, and a number of small nucleolar RNAs and microRNAs (1). In the yeast Saccharomyces cerevisiae, the Pol III transcription apparatus consists of 17-subunit Pol III and three other transcription factors: single-polypeptide TFIIIA, three-subunit TFIIIB, and six-subunit TFIIIC (2, 3). TFIIIA and TFIIIC function as the promoter recognition factors, and TFIIIB is recruited to the promoter through TFIIIC. TFIIIB is composed of TFIIB-related factor Brf1, TATA box binding protein TBP, and SANT domain-containing subunit Bdp1. Previous biochemical studies indicated that Brf1 and TBP cooperatively assemble onto DNA upstream of the transcription start site and Bdp1 binds to the Brf1-TBP-DNA complex mainly through its SANT domain (4-10). The TFIIIB-DNA assembly is required for subsequent Pol III recruitment and transcript initiation. Both Brf1 and Bdp1 have been found to interact with Pol III and function in promoter opening (4,(11)(12)(13)(14).The N-terminal domain of yeast Brf1 (Brf1n; amino acids [aa] 1 to 286) contains a zinc ribbon fold (aa 3 to 34) and a cyclin fold repeat subdomain (aa 83 to 282) (Fig. 1A), both of which are homologous to those in the general transcription factor TFIIB of the Pol II system. On the basis of biochemical and structural analyses, TFIIB ribbon and cyclin fold repeats are, respectively, positioned in the RNA exit tunnel and in the wall domain of Pol II (15)(16)(17)(18)(19)(20). In addition, the connecting region between the TFIIB ribbon and the cyclin repeat domain has been structurally resolved to contain B reader and B linker motifs that interact with the Pol active center. On the basis of sequence comparison, the connecting region in Brf1n, which we refer to as the N linker, contains low sequence homology ...

Rpc82 is a TFIIE-related subunit of the eukaryotic RNA polymerase III (pol III) complex. Rpc82 contains four winged-helix (WH) domains and a C-terminal coiled-coil domain. Structural resolution of the pol III complex indicated that Rpc82 anchors on the clamp domain of the pol III cleft to interact with the duplex DNA downstream of the transcription bubble. However, whether Rpc82 interacts with a transcription factor is still not known. Here, we report that a structurally disordered insertion in the third WH domain of Rpc82 is important for cell growth and in vitro transcription activity. Site-specific photo-crosslinking analysis indicated that the WH3 insertion interacts with the TFIIB-related transcription factor Brf1 within the pre-initiation complex (PIC). Moreover, crosslinking and hydroxyl radical probing analyses revealed Rpc82 interactions with the upstream DNA and the protrusion and wall domains of the pol III cleft. Our genetic and biochemical analyses thus provide new molecular insights into the function of Rpc82 in pol III transcription.