The active site in AcpS is only formed when two AcpS molecules dimerize. The addition of a third molecule allows for the formation of two additional active sites and also permits a large hydrophobic surface from each molecule of AcpS to be buried in the trimer. The mutations Ile5-->Arg, Gln113-->Glu and Gln113-->Arg show that AcpS is inactive when unable to form a trimer. The co-crystal structures of AcpS-CoA and AcpS-ACP allow us to propose a catalytic mechanism for this class of 4'-phosphopantetheinyl transferases.

TCR-driven interactions determine the lineage choice of CD4+CD8+ thymocytes, but the molecular mechanisms that induce the lineage-determining transcription factors are unknown. Here we show that TCR-induced Egr2 and Egr1 proteins had elevated and prolonged expression in NKT lineage precursors compared with conventional lineages. ChIP-seq analysis uncovered that Egr2 directly bound and activated the promoter of Zbtb16 which encodes the NKT lineage-specific transcription factor PLZF. Egr2 also bound the Il2rb promoter and controlled the responsiveness to IL-15, which signals the terminal differentiation of the NKT lineage. Thus, we propose that elevated and persistent Egr2 levels specify the early and late stages of NKT lineage differentiation, providing a discriminating mechanism that enables TCR signaling to instruct a thymic lineage.

SUMMARY Microcephaly is a neurodevelopmental disorder causing significantly reduced cerebral cortex size. Many known microcephaly gene products localize to centrosomes, regulating cell fate and proliferation. Here, we identify and characterize a nuclear zinc finger protein, ZNF335/NIF-1, as a causative gene for severe microcephaly, small somatic size, and neonatal death. Znf335-null mice are embryonically lethal and conditional knockout leads to severely reduced cortical size. RNA-interference and postmortem human studies show that Znf335 is essential for neural progenitor self-renewal, neurogenesis, and neuronal differentiation. ZNF335 is a component of a vertebrate-specific, trithorax H3K4-methylation complex, directly regulating REST/NRSF, a master regulator of neural gene expression and cell fate, as well as other essential neural-specific genes. Our results reveal ZNF335 as an essential link between H3K4 complexes and REST/NRSF, and provide the first direct genetic evidence that this pathway regulates human neurogenesis and neuronal differentiation.