E3 ubiquitin-protein ligase that monoubiquitinates H2B to form H2BK143ub1. H2BK143ub1 gives a specific tag for epigenetic transcriptional activation and is a prerequisite for H3 Lys-4 methylation (H3K4me). It thereby plays a central role in histone code and gene regulation. H2B monoubiquitination (H2BK143ub1), mediated by HUB1, modulates transcriptional regulation of anther development, likely by promoting histone H3K4 dimethylation (H3K4me2) in the chromatin of the key tapetum degradation-related genes C4, CP1 and UDT1. S-ubiquitinyl-[E2 ubiquitin-conjugating enzyme]-L-cysteine + [acceptor protein]-L-lysine = [E2 ubiquitin-conjugating enzyme]-L-cysteine + N(6)-ubiquitinyl-[acceptor protein]-L-lysine. Protein modification; protein ubiquitination. Interacts with SKIPA (PubMed:19339499). Interacts with HUB2 (PubMed:26143250). The RING-type zinc finger domain mediates binding to an E2 ubiquitin-conjugating enzyme. Semi-dwarf plants, early heading, and partial sterility of spikelets due to defects in the anther developmental program and pollen formation. Belongs to the BRE1 family. Due to a cryptic acceptor splice site.