組織蛋白 (histones) H1、H2A、H2B、H3和H4是與DNA結合的蛋白質，幫助DNA摺疊形成染色質。組織蛋白經由各種後修飾作用去調節DNA的轉錄、複製及修復，像是經由磷酸化、乙酰化，生物素化和ADP-核糖基化的過程。其中一種後修飾作用是加上生物素，經由生物素蛋白連接酶 (biotin protein ligase) 以共價鍵的方式將生物素加在蛋白質的離胺酸 (lysine residues)上。在細胞生長和脂肪酸代謝中生物素是必要的，當作乙醯輔酶A羧化酶 (acetyl-CoA carboxylase) 和丙酮酸羧化酶 (pyruvate carboxylase) 的輔助因子。在羧化酶 (carboxylases) 中有一段保守序列AMKM，其中的離胺酸會被加上生物素。由先前文獻得知，生物素化可發生在不同的物種中。令人驚奇的是在白色念珠菌 (Candida albicans) 中的組織蛋白H2A、 H2B和H4缺乏保守序可提供生物素蛋白連接酶辨認，但是這物種卻可以把生物素加到組織蛋白上，而這些生物素的位置也沒有固定的序列。由本研究得知，H2B被加上生物素會受生物素的濃度以及溫度影響。此外，在體外和體內實驗中，白色念珠菌的生物素蛋白連接酶無法將釀酒酵母菌 (Saccharomyces cereviseae) 的H2B進行生物素化的反應。本研究進一步目的是為了探討白色念珠菌的生物素蛋白連接酶的受質專一性如何進行生物素化的反應機制。

Histones H1, H2A, H2B, H3 and H4 are DNA-binding proteins that mediate the folding of DNA into chromatin. Various posttranslational modifications of histones such as phosphorylation, acetylation, ubiquitinylation and ADP-ribosylation regulate processes such as transcription, replication and repair of DNA. One of the posttranslational modifications is biotinylation, which is covalent binding of biotin to lysine residues of a protein, mediated by biotin protein ligase (Bpl1p). Biotin is required for cell growth and fatty acid metabolism. It is used as a cofactor for carboxylases such as acetyl-CoA carboxylase and pyruvate carboxylase. The biotinylated lysine residue is almost invariably positioned in a consensus sequence, AMKM, within carboxylases. As a result, biotinylation can occur across widely divergent species. Paradoxically, the histones H2A, H2B and H4 of Candida albican lack a consensus sequence, but can be bioyinylated by its own biotin protein ligase (Bpl1p) in vivo. In addition, biotinylation of these histone proteins is non site specific. In this study, we showed that biotinylation of H2B is biotin concentration dependent and temperature dependent. Moreover, the Bpl1p of C. albicans failed to biotinylate the histone proteins of Saccharomyces cereviseae in vivo and in vitro. More studies are underway to elucidate the specificity and mechanism of biotinylation by C. albican Bpl1p.

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