events.

2x3 Gene. 103 ( 199 1 ) 2x3-2x3

#cl 1991 Elscvicr Scicncc Publishers B.V. All rights reserved. 0378-l 1141’9 1:$03.50

GENE OiO39

Brief Notes

Characterization of Alu repeats surrounding the human ferredoxin-encoding gene

(Direct repeats; retroposition; evolution; gene family; pseudogene; steroidogenesis)

Chi-Yao Chang”Tb and Bon-chu Chung”

” Institute of Molecular Biology, Academia Sinica. Nankang, Taipei, T’aiwan, 11529, Republic of China, and h Institute of Life Sciences, Tsing-Hwa CJniversit>~. Hsin-Chu. Taiwan, Republic of China

Received by A.-M. Skalka: 26 March 1991 Revised: 16 April lY91 Accepted: 30 April 1991

SUMMARY

Three A/u sequences have been identified surrounding the human ferredoxin-encoding genes. Among them, one is located

about 1000 bp upstream from the active gene, whereas two others flank the ferredoxin pseudogene, YFDX3. All these A/u

sequcnccs contain poly(A) tails and are flanked by direct repeats, indicating that they arose by RNA-mediated transposition

Ferredoxin is an iron-sulfur-containing protein that

serves as an electron donor in the oxidation/reduction

reactions catalyzed by the mitochondrial cytochromes

P-450 (Nakamura and Otsuka, 1966). It functions in the

synthesis of steroids, bile acid, and vitamin D (Waterman

et al., 1986). Its synthesis is stimulated by CAMP in various

tissues at the transcriptional level (Anderson and

Mendelson, 1985; Golos et al., 1987; John et al., 1986;

Kramer et al., 1982; Picado-Leonard et al., 1988). The

human FDX gene family contains two pseudogenes, YFDX2

and YFDX3, in addition to the active FDX 1 gene (Chang

et al., 1990). We have studied the genomic organization

surrounding the FDX gene and noted three Al~l sequences

(Fig. 1). One is present at about 1000 bp upstream from the

active gene, termed h5-Alu. The others are each located

about 100 bp upstream and downstream from YFDX3,

termed h3-5’-Aiu and h3-3’-A/u repeats.

When examining h3-Alu sequences, we find that

h3-3’-Alu is flanked by 7-bp perfect repeats and h3-5’-A/u

by 12-bp imperfect repeats (Fig. 2). These Afu sequences

again have poly(A) tails at their 3’-ends. These features

indicate that they arose as a result of RNA-mediated trans-

position (Schmid and Jelinek, 1982). The YFDX3

pseudogene also contains similar features and is presum-

ably generated through similar retroposition events (Chang

et al., 1990).

The h5-Alu lacks the left half of the Ah4 repeat. A typical

Alu is composed of two monomers. The first monomer is

about 120 bp in length, the second one is about 150 bp in

length with a 31-bp insertion (Schmid and Jelinek, 1982).

The h5-Alu contains only the right half with a poly(A) tail.

This half-A/u sequence was probably inserted into the chro-

mosome through RNA-mediated events, since it was

flanked by S-bp imperfect direct repeats (Fig. 2). The pres-

ence of h5-Alu in the 5’-flanking region of the human FDX

gene makes this region divergent from the otherwise homol-

ogous sequence in the upstream region of the bovine FDX

gene (Sagara et al., 1990). These features make the human

FDX gene distinct from the FDX gene in other species and

may represent an important evolutionary event.

Correspondence to: Dr. B.-c. Chug. Institute of Molecular Biology,

Academia Sinica, Nankang, Taipei, Taiwan, 11529 Republic of China

Tel. (X86-2)-789-9215; Fax (886-2).782-6085.

Abbreviations: bp, base pair(s); FDX, gene(s) encoding ferredoxin; kb,

kilobase or 1000 bp; Y, pseudogene.

ACKNOWLEDGEMENTS

This work was supported by National Science Council,

NSC-78-0203-BOOl-11 and Academia Sinica, Republic

of China.

A. h5-Alu

h3

h3-5’- A/U YFDx3 3’-UT

h3-3’- A/U

L R L R L R

L BAAAATATAACAT L 1 TCAGTGA L T-iTTGAA 0

R ~AAAATTTA-CAT RI TCAGTGA R [mGAA

B

h5

h5-A/u FDX exon 1

L 1 AAAAATTA 100 bp

R 1 AAAAAGTA H

t‘Ip_ I. Structure of .4/u repcats surrounding the human b’I1.v genes.

(A) ‘4114 repeats flanking ‘YFDX3. (B) A/u at the 5’-upstream region ofthe

cxprcssed FD.Y gene. A and B: lines represent intergenic sequences.

Shaded boxes indicate coding regions and the hatched bower represent

untranslated regions. ‘The arrows indicate the orientation of the ,4hr

scqucnccs. Four kinds of boxes above 1. or R Indicate direct rcpeatr.

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