length. HDAC6 is the only HDAC to be shown to act on tubulin, acting as a tubulin deacetylase which helps in the regulation of microtubule-dependent cell motility. It is mostly found in the cytoplasm but has been known to be found in the nucleus, complexed together with HDAC11. HDAC10 has been seen to act on HDACs 1, 2, 3 (or SMRT), 4, 5 and 7. Some evidence has been shown that it may have small interactions with HDAC6 as well. This leads researchers to believe that HDAC10 may function more as a recruiter rather than a factor for deacetylation. However, experiments conducted with HDAC10 did indeed show deacetylation activity. Class IV HDACs HDAC11 HDAC11 has been shown to be related to HDACs 3 and 8, but its overall sequence is quite different from the other HDACs, leading it to be in its own category. HDAC11 has a catalytic domain located in its N-terminus. It has not been found incorporated in any HDAC complexes such as Nurd or SMRT which means it may have a special function unique to itself. It has been found that HDAC11 remains mainly in the nucleus. Biological functions Transcription regulation The discovery of histone acetylation causing changes in transcription activity can be traced back to the work of Vicent Allfrey and colleagues in 1964. The group hypothesized that histone proteins modified by acetyl groups added negative charges to the positive lysines, and thus, reduced the interaction between DNA and histones. Histone modification is now considered a major regulatory mechanism that is involved in many different stages of genetic functions. Our current understanding is that acetylated lysine residues on histone tails is associated with transcriptional activation. In turn, deacetylated histones are associated with transcriptional repression. In addition, negative correlations have been found between several histone acetylation marks. The regulatory mechanism is thought to be twofold. Lysine is an amino acid with a positive charge when unmodified. Lysines on the amino terminal tails of histones have a tendency to weaken the chromatin's overall structure. Addition of an acetyl group, which carries a negative charge, effectively removes the positive charge and hence, reduces the interaction between the histone tail and the nucleosome. This opens up the usually tightly packed nucleosome and allows transcription machinery to come into contact with the DNA template, leading to gene transcription. Repression of gene transcription is achieved by the reverse of this mechanism. The