|
||
Genes
By
From the Laboratory of Cell and Viral Regulation, Division of Hematologic Products, Center for
Biologics Evaluation and Research, Food and Drug Administration, Bethesda, Maryland 20892
To investigate regulation of human immunoglobulin heavy chain expression, we have cloned
DNA downstream from the two human C
genes, corresponding to the position in the mouse
IgH cluster of a locus control region (LCR) that includes an enhancer which regulates isotype
switching. Within 25 kb downstream of both the human immunoglobulin C
1 and C
2 genes
we identified several segments of DNA which display B lymphoid-specific DNase I hypersensitivity as well as enhancer activity in transient transfections. The corresponding sequences
downstream from each of the two human C
genes are nearly identical to each other. These
enhancers are also homologous to three regions which lie in similar positions downstream from
the murine C
gene and form the murine LCR. The strongest enhancers in both mouse and
human have been designated HS12. Within a 135-bp core homology region, the human HS12
enhancers are ~90% identical to the murine homolog and include several motifs previously
demonstrated to be important for function of the murine enhancer; additional segments of high
sequence conservation suggest the possibility of previously unrecognized functional motifs. On
the other hand, certain functional elements in the murine enhancer, including a B cell-specific
activator protein site, do not appear to be conserved in human HS12. The human homologs of
the murine enhancers designated HS3 and HS4 show lower overall sequence conservation, but
for at least two of the functional motifs in the murine HS4 (a
B site and an octamer motif ) the
human HS4 homologs are exactly conserved. An additional hypersensitivity site between human HS3 and HS12 in each human locus displays no enhancer activity on its own, but includes
a region of high sequence conservation with mouse, suggesting the possibility of another novel
functional element.
This article has been cited by other articles:
| TABLE OF CONTENTS |
|