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Isolation and characterization of the cDNAs
To search for transcripts in the region covered by the contig, genomic fragments (Fig.2),
were used to screen a fetal brain cDNA library (Clontech, HLl065). Sequence analysis and
restriction mapping of the isolated cDNA clones proved that all clones were derived from the
same gene and one of them (cDNA 17.1) contained a poly (A) tail with a polyadenylation
signal 22 bp upstream. In total about 3 kb of the cDNA was isolated. The insert isolated
from one of these clones, cDNA probe 17.1, was used on a northern blot and recognized a
messenger of approximately 8 kb (Fig. 4). Therefore, the previous and another cDNA library
(Stratagene 936206) were screened again with probes located at the most 5' end from former
screens, Some clones derived from the second library contained composite inserts and
therefore were discarded unless carefully checked. Tn total overlapping cDNAs were isolated
which together span approximately 7.5 kb of the messenger. We do not know yet if we
isolated a full-length cDNA. We have called the gene from which these cDNAs were derived
MNI.
Restriction mapping of cDNA clones and subcloned genomic fragments from this
region showed that the isolated 7.5 kb transcript consists of two large exons of 4.7 kb at the
5' end and 2.8 kb at the 3' end (data not shown). The 5' exon-intron boundary was
sequenced and revealed a consensus splice acceptor site (data not shown), The localization
of the gene on the isolated chromosome 22 contig is depicted in figure 2 and shows that the
gene spans approximately 70 kb and is interrnpted by one 60 kb intron.
Mapping of the tmnsloeation bl'eakpoint
Fine mapping of the breakpoint was done on mapping panels with 2 genomic probes and a
cDNA probe located in the 8 kb genomic EcoRI fragment in which the breakpoint was found
(Fig. 3). EcoRI restriction patterns obtained with these probes on DNA extracted from
cultured meningioma 32 tumor cells (MN32), hybrids harbouring the 22q- (6A) or 4p+
(l4G-IO) marker chromosomes of meningioma 32 and controls (human, 9B, A3, PgMe25Nu
and mouse) are shown in figure 3. Genomic probe A, located at the tclomeric site of this 8
kb genomic fragment, detects in addition to the normal 8 kb band an aberrant band of 7 kb
in meningioma 32 DNA (Fig. 3A, lane MN32). The 8 kb band corresponds to hybridization
with the other copy of chromosome 22 present in the tumor. The aberrant band is the result
of hybridization with the breakpoint containing fragment on the 4p+ marker. Furthermore,
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