LR1 is a B cell-specific, sequence-specific DNA binding activity that regulates transcription in activated B cells. LR1 also binds Ig heavy chain switch region sequences and may function in class switch recombination. LR1 contains two polypeptides, of 106 kDa and 45 kDa, and here we report that the 106-kDa component of LR1 is nucleolin. This identification, initially made by microsequence analysis, was verified by showing that (i) LR1-DNA binding activity increased in B cells transfected with a nucleolin cDNA expression construct; (ii) LR1-DNA binding activity was recognized by antibodies raised against recombinant human nucleolin; and (iii) in B cells transfected with epitope-tagged nucleolin expression constructs, the LR1-DNA complex was recognized by the anti-tag antibody. Nucleolin is an abundant nucleolar protein which is believed to play a role in rDNA transcription or organization, or rRNA processing. Homology between nucleolin and histone H1 suggests that nucleolin may alter DNA organization in response to cell cycle controls, and the nucleolin component of LR1 may therefore function to organize switch regions before, during, or after switch recombination. The demonstration that nucleolin is a component of a B cell-specific complex that binds switch region sequences suggests that the G-rich switch regions may have evolved from rDNA.LR1 is a B cell-specific, sequence-specific DNA binding activity. It was first identified as a factor that specifically recognizes Ig switch region sequences and is induced in primary B cells activated to carry out class switch recombination (1, 2). LR1 has also been shown to regulate transcription of two genes that function in B cell transformation, c-myc (3) and the Epstein-Barr virus EBNA-1 gene (4).In Ig switch recombination, one constant region is literally switched for another by joining a rearranged and expressed variable region to a downstream constant region, deleting a long region of intervening DNA. Switching involves repetitive, G-rich regions of DNA, called switch regions (S regions), that are found upstream of the constant regions that undergo switch recombination (5-7). A specific S region is targeted for recombination by induction of noncoding transcripts from a promoter upstream of that S region (8-14), and recombination depends on both transcription and splicing of these switch transcript (15). Since S region transcription is prerequisite to recombination, it is possible that LR1 binding to sites in the S regions might potentiate S region transcription and thereby activate recombination. In vitro DNA binding studies have shown that the LR1-DNA binding consensus, GGNC-NAG(G͞C)CTG(G͞A), is loose, and LR1 may bind multiple sites in each of the G-rich S regions. This suggests that another possible function for LR1 could be to organize S region DNA before, during, or after recombination.To understand the function of LR1, we have purified and characterized the activity. LR1 is a complex of two polypeptides, of 106 kDa and 45 kDa (2, 16). In this communicati...

No abstract

The immunoglobulin heavy chain switch regions contain multiple runs of guanines on the top (nontemplate) DNA strand. Here we show that LR1, a B cell-specific, duplex DNA binding factor, binds tightly and specifically to synthetic oligonucleotides containing G-G base pairs (K D < 0.25 nM). LR1 also binds to single-stranded G-rich sequences (K D Ϸ 10 nM). The two subunits of LR1, nucleolin and hnRNP D, bind with high affinity to G4 DNA (K D ‫؍‬ 0.4 and 0.5 nM, respectively). LR1 therefore contains two independent G4 DNA binding domains. We propose that LR1 binds with G-G-paired structures that form during the transcription of the S regions that is prerequisite to recombination in vivo. Interactions of donor and acceptor S regions with subunits of the LR1 could then juxtapose the switch regions for recombination.

We present the first three-dimensional, functional images of the human brain to be obtained using a fibre-less, high-density diffuse optical tomography system. Our technology consists of independent, miniaturized, silicone-encapsulated DOT modules that can be placed directly on the scalp. Four of these modules were arranged to provide up to 128, dual-wavelength measurement channels over a scalp area of approximately 60 × 65 mm2. Using a series of motor-cortex stimulation experiments, we demonstrate that this system can obtain high-quality, continuous-wave measurements at source-detector separations ranging from 14 to 55 mm in adults, in the presence of hair. We identify robust haemodynamic response functions in 5 out of 5 subjects, and present diffuse optical tomography images that depict functional haemodynamic responses that are well-localized in all three dimensions at both the individual and group levels. This prototype modular system paves the way for a new generation of wearable, wireless, high-density optical neuroimaging technologies.