Recombinant and in vitro expression systems for hydrogenases: new frontiers in basic and applied studies for biological and synthetic H2 production.

This review focuses on recent progress in developing heterologous and recombinant expression as well as in vitro maturation systems for the biosynthesis of active [FeFe] and [NiFe]-hydrogenases, which catalyze the reversible reaction, H2 <--> 2e- + 2H+. Activities of [FeFe] and [NiFe]-hydrogenases produced from different recombinant and in vitro maturation approaches are compared. Examples of how hydrogenase expression supports basic and applied studies of these enzymes are presented, and barriers to achieving more viable biological and synthetic H2-production systems and catalysts are addressed.

The histone chaperone anti-silencing function 1 stimulates the acetylation of newly synthesized histone H3 in S-phase.

Anti-silencing function 1 (Asf1) is a highly conserved chaperone of histones H3/H4 that assembles or disassembles chromatin during transcription, replication, and repair. We have found that budding yeast lacking Asf1 has greatly reduced levels of histone H3 acetylated at lysine 9. Lysine 9 is acetylated on newly synthesized budding yeast histone H3 prior to its assembly onto newly replicated DNA.

Structural basis for the histone chaperone activity of Asf1.

Anti-silencing function 1 (Asf1) is a highly conserved chaperone of histones H3/H4 that assembles or disassembles chromatin during transcription, replication, and repair. The structure of the globular domain of Asf1 bound to H3/H4 determined by X-ray crystallography to a resolution of 1.7 Angstroms shows how Asf1 binds the H3/H4 heterodimer, enveloping the C terminus of histone H3 and physically blocking formation of the H3/H4 heterotetramer.

ASF1 binds to a heterodimer of histones H3 and H4: a two-step mechanism for the assembly of the H3-H4 heterotetramer on DNA.

The first step in the formation of the nucleosome is commonly assumed to be the deposition of a histone H3-H4 heterotetramer onto DNA. Antisilencing function 1 (ASF1) is a major histone H3-H4 chaperone that deposits histones H3 and H4 onto DNA. With a goal of understanding the mechanism of deposition of histones H3 and H4 onto DNA, we have determined the stoichiometry of the Asf1-H3-H4 complex.