https://youtu.be/Ue6Hx6MqATw video link A proposed method of transmitting gene expression instructions through cell division is known as bookmarking. What is the importance of gene bookmarking When bookmarking is done Criteria for gene bookmarking Mechanism of gene bookmarking Example of gene bookmarking Gene Bookmarking by the Heat-Shock Transcription Factor

1. BOOKMARKING

2. INTRODUCTION
MECHANISM OF GENE
BOOKMARKING

3. Introduction
01

4. Cells have several mechanisms for regulating
transcription that are based on modulation of
chromatin structure near specific genes.
These mechanisms include:
‫؀‬ Remodeling of chromatin
‫؀‬ Differential methylation of specific DNA regions
‫؀‬ There is, however, another mechanism that is
crucial for proper gene expression – termed
gene bookmarking – about which much less is
known.
Introduction

5. Gene
Bookmarking
The process of remembering patterns of
active gene expression during mitosis for
transmission to daughter cells is called
gene bookmarking

7. ⮚ Some genes like hsp70 gene that are essential for protecting the cells from
stress must be activated as early as possible during or just after the
completion of mitosis.
⮚ During mitosis the transcription is in the state of repression. So if these
essential genes were not bookmarked, the cell might not be able to
transcribe until normal decompaction process were complete, which will
take some time after mitosis.
⮚ Such a delay in transcription might lead to the disruption of cell function or
even cell death.
Example

8. Criteria
At some point prior to the onset of mitosis,
the promoters of genes that exist in
a transcription-competent state become
"marked" in some way,
This "mark" persists both during and after
mitosis, and
The marking transmits gene expression
memory by preventing the mitotic compaction
of DNA at this locus, or by facilitating
reassembly of transcription complexes on
the promoter, or both.

9. MECHANISM of gene
bookmarking
02

10. Mechanism of gene
bookmarking
Mechanisms
of gene
bookmarking
:
modification of
histones
The persistent
binding of TFIID
complexes to
promoter

11. 1. Modification of histone
● 'memory' of gene expression patterns could
be propagated to daughter cells because of
the modification of histones at the regions
corresponding to active genes.
● hyperacetylation of histone H3 and H4,
● demethylation of Lys4 and Lys79 on histone
H3 and
● trimethylation of Lys4 on histone H3 were
found as evidence to support this
hypothesis.

12. 2. The persistent binding of TFIID complexes
to promoter
●TFIID transcription factor its associated protein complexes interact
with TATA box.
●In mitotic cells, TFIID along with TFIIB remain associated with the
promoters off genes that are active in cells but not with inactive genes.
These results support the hypothesis of TFIID as a good candidate for
bookmarking the promoters of active genes.
●By using TFIID transcription factor for bookmarking, the cells can
easily identify the active genes

13. ●HSP70 is an important cyto-protective protein
upregulated during stress, mediated by HSF1
transcription factor.
●Stress plays an important role in converting HSF1
into its DNA - binding form. HSF1 interacts with
HSEs in the hsp70 promoter and increases its rate
of transcription.
● These HSE elements are located in a region of the
hsp70 promoter that contains sites showing
persistent hypersensitivity to DNAase in mitotic
cells, suggesting that it is a part of the
bookmarked region.
HSP70 Promoter in Bookmarking