3.2 │ Localization of histone H1 subtypes interacting proteins
Localization of histone H1 subtypes partnering proteins was determined
with highest localization score indicated in the ComPPI database. As it
was shown in the Figure 3, the main subcellular compartment in which the
proteins are located is nucleus and cytosol, characteristic of
46.0–65.0% and 22.0–40.0% proteins, respectively. Although no
statistically significant difference in the localization of histone H1
subtypes partnering proteins was detected (F = 0.0052, p =
0.999), a disproportions of their emplacement shows on a diverse
engagement of histone H1 subtypes in the processes running in the
nucleus and cytosol. Whereas histone H1.1 have 65.0% of partner
proteins located in the nucleus and 22.0% characteristic of a cytosol,
it should be perceived as more active in the nucleus. In contrast, the
histone H1.2, possessing 48.0% partnering proteins in the nucleus and
40.0% in the cytosol, might be similarly active in both regions of the
cell. Likewise, almost twice more histone H1.4 interacting proteins
originating from nucleus (59.0%) than from cytosol (30%) indicate that
this histone H1 subtype may play more significant role in the nucleus.
On the contrary, a participation of histone H1.3 in the processes
running in the nucleus (46.0% partnering proteins) and in the cytosol
(36.0% partnering proteins) can be considered as comparable. Other
proteins interacting with histone H1 subtypes are the components of
membrane, mitochondrion and secretory pathway and also remain in both
nucleus and cytosol. Such a locations are generally characteristic of
less than 5% of proteins, except for these which are the partners of
histone H1.1 located in both nucleus and cytosol (6.0%) as well as the
membrane proteins (10.0%) interacting with histone H1.3. Besides, a
comparable proportions of the secretory pathway proteins designated as
the partners of histone H1.1 – H1.4 (1.0 - 2.0%) differ from an amount
of proteins predicted as interacting with histone H1.5 (9%). This
suggest a stronger relationship of histone H1.5 with function of the
endoplasmic reticulum and Golgi apparatus. Although a complete
wide-genome distribution of H1 subtypes still needs to be definitively
determined, a known reports regarding localization of H1 histones point
to their association with a specific chromatin type and, thus, a
characteristic role in chromatin-dependent cellular processes. Based on
the findings of Izzo et al. 26, a disparate abundance
of histone H1.1 and histone H1.2 – H1.5 are discernible at promoters,
enhancers and CpG islands. Histone H1.1 is preferentially located in the
PcG regions marked by H3K9me3 while histone H1.2 – H1.5 in the
HP1-containing domains marked by H3K27me3. Thus, in contrast to the
subtype H1.2 – H1.5, subtype H1.1 has more potential to form both
active and repressed chromatin state. In another study27, a difference in emplacement in the genome was
detected between histone H1.2 and other H1 subtypes. Whereas histone
H1.0 and H1X was detected as associated with high CG content and
gene-rich regions, histone H1.2 was indicated as located in the regions
with low CG content and gene-poor. These reports pointing to peculiar
distribution of histone H1 subtypes reflects simultaneously their
differential influence on processes running in the chromatin. It seems
that a similar relationship may concern the activity of histone H1
subtypes differently realized in various cell structures through their
interaction with partner proteins.