High impact information on B52

• We have used indirect immunofluorescence of polytene chromosomes to examine the chromatin distribution of a 52-kD Drosophila protein designated B52 [1].
• The predicted primary amino acid sequence of B52 reveals two regions with similarities to a number of other proteins known to interact with nucleic acids [1].
• The RS domain of dU2AF50 functioned efficiently, while that of the dSRp55 protein did not [2].
• Additional cDNA clones reflect extensive alternative splicing of SRp40 and SRp55 pre-mRNAs [3].
• It binds B52 in vivo and suppresses all phenotypes caused by B52 overexpression [4].

Biological context of B52

• Thus, B52 is an essential gene and has a critical role in Drosophila development [5].
• Microarray analyses revealed that many transcripts involved in brain organogenesis have altered splicing profiles upon both loss and gain of B52 function [6].
• Almost all of the corresponding genes having a known function encode either transcription factors or components of signal transduction pathways, with the B52- binding fragments located to not only exonic but also intronic regions [7].
• These results indicate that B52 has unique functions in the removal of some introns during development, and plays a critical role in cellular regulatory networks [7].
• Drosophila SRp55 also functions as an alternative splicing factor in the human cell-free system [8].

Anatomical context of B52

• Germ line transformation of Drosophila flies with B52 genomic DNA rescues this lethality [5].

Associations of B52 with chemical compounds

• The omegaspeckles are distinct from interchromatin granules since nuclear speckles containing serine/arginine-rich SR-proteins like SC35 and SRp55 did not colocalize with the &ohgr; speckles [9].
• In Chironomus tentans, hrp45 is an SR protein structurally similar to the Drosophila SRp55/B52 SR protein [10].

Other interactions of B52

• The resulting deletion, B52(28), is confined to the B52 gene and its neighbor the Hrb87F gene [5].
• Moreover, Kc cell nuclear extracts that were immunodepleted of B52 lost their ability to splice this ftz pre-mRNA [11].
• Reexpression of the intronless copy of dE2F2 in B52-deficient cells restores the dE2F2-mediated repression [12].

Analytical, diagnostic and therapeutic context of B52

• We have also examined the distribution of B52 on nonpolytene chromosomes in Drosophila cell cultures with an in vivo UV cross-linking method and find that, here too, B52 is associated with boundaries of transcriptionally active chromatin [1].

References