Translation_control_of_nanos_mRNA_by_Smaug_protein

Smaug is a

RNA-binding protein RNA-binding proteins (often abbreviated as RBPs) are proteins that bind to the double or single stranded RNA in cells and participate in forming ribonucleoprotein complexes. RBPs contain various structural motifs, such as RNA recognition motif ...

in ''

Drosophila ''Drosophila'' () is a genus of flies, belonging to the family Drosophilidae, whose members are often called "small fruit flies" or (less frequently) pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many speci ...

'' that helps in

maternal to zygotic transition Maternal to zygotic transition (MZT, also known as Embryonic Genome Activation) is the stage in embryonic development during which development comes under the exclusive control of the zygotic genome rather than the maternal (egg) genome. The egg co ...

(MZT). The protein is named after the fictional character

Smaug Smaug () is a dragon and the main antagonist in J. R. R. Tolkien's 1937 novel ''The Hobbit'', his treasure and the mountain he lives in being the goal of the quest. Powerful and fearsome, he invaded the Dwarf kingdom of Erebor 150 years prior ...

, the dragon in J.R.R. Tolkien's 1937 novel ''

The Hobbit ''The Hobbit, or There and Back Again'' is a children's fantasy novel by English author J. R. R. Tolkien. It was published in 1937 to wide critical acclaim, being nominated for the Carnegie Medal and awarded a prize from the ''N ...

''. The MZT ends with the midblastula transition (MBT), which is defined as the first developmental event in ''Drosophila'' that depends on zygotic mRNA. In ''Drosophila'', the initial developmental events are controlled by maternal mRNAs like ''Hsp83'', '' nanos'', ''string'', ''Pgc'', and ''

cyclin B Cyclin B is a member of the cyclin family. Cyclin B is a mitotic cyclin. The amount of cyclin B (which binds to Cdk1) and the activity of the cyclin B-Cdk complex rise through the cell cycle until mitosis, where they fall abruptly due to degra ...

'' mRNA. Degradation of these mRNAs, which is expected to terminate maternal control and enable zygotic control of embryogenesis, happens at interphase of nuclear division cycle 14. During this transition smaug protein targets the maternal mRNA for destruction using miRs. Thus activating the zygotic genes. Smaug is expected to play a role in expression of three miRNAs – ''miR-3, miR-6, miR-309'' and ''miR-286'' during MZT in ''Drosophila''. Among them smaug dependent expression o
''miR-309''
is needed for destabilization of 410 maternal mRNAs. In smaug mutants almost 85% of maternal mRNA is found to be stable. Smaug also binds to 3′ untranslated region (UTR) elements known as ''SMG response elements'' (SREs) on ''nanos'' mRNA and represses its expression by recruiting a protein calle
Cup
''(an eIF4E-binding protein that blocks the binding of

eIF4G Eukaryotic translation initiation factor 4 G (eIF4G) is a protein involved in eukaryotic translation initiation and is a component of the eIF4F cap-binding complex. Orthologs of eIF4G have been studied in multiple species, including humans, yeas ...

eIF4E Eukaryotic translation initiation factor 4E, also known as eIF4E, is a protein that in humans is encoded by the ''EIF4E'' gene. Structure and function Most eukaryotic cellular mRNAs are blocked at their 5'-ends with the 7-methyl-guanosine f ...

)''. There after it recruits deadenylation complex

CCR4-Not Carbon Catabolite Repression—Negative On TATA-less, or CCR4-Not, is a multiprotein complex that functions in gene expression. The complex has multiple enzymatic activities as both a poly(A) 3′-5′ exonuclease and a ubiquitin ligase. The com ...

on to the nanos mRNA which leads to

deadenylation Polyadenylation is the addition of a poly(A) tail to an RNA transcript, typically a messenger RNA (mRNA). The poly(A) tail consists of multiple adenosine monophosphates; in other words, it is a stretch of RNA that has only adenine bases. In euk ...

and subsequent decay of the mRNA.{{Cite journal, last1=Zaessinger, first1=Sophie, last2=Busseau, first2=Isabelle, last3=Simonelig, first3=Martine, date=November 2006, title=Oskar allows nanos mRNA translation in Drosophila embryos by preventing its deadenylation by Smaug/CCR4, journal=Development , volume=133, issue=22, pages=4573–4583, doi=10.1242/dev.02649, issn=0950-1991, pmid=17050620, doi-access=free It is also found to be involved in degradation and repression of materna
Hsp83
mRNA by recruiting CCR4/POP2/NOT deadenylase to the mRNA. The human Smaug protein homologs are SAMD4A and SAMD4B.

References

External links

Mechanisms of the ''Drosophila'' Mid-blastula Transition

Hsp83 Heat shock protein 83

smg- Protein Smaug - Drosophila by Uniprot
RNA-binding proteins Things named after Tolkien works