Table 1.

Overview of Mutant Alleles^[Note]

No. of Alleles	cDNA	Genomic DNA	Restriction- Site Changea	Observed mRNA Changeb	Deduced AminoAcid Change	Activity in E. colic	Decreased or PresentCBS Immunodetection in E. coli	Referencesd
7	c.833 T→C	g.9122 T→C	BsrI+		I278T	0–1.5	Decreased	1
7	IVS11−2A→C	g.13217 A→C	MspI+	c.1224_1358del135	W409_G453del	0	Decreased	1
3	c.19_20insC	g.19_20insC	Mwo I−e		P6fsX36	ND	ND
2f	[c.430 G→A; c.463G→A]	[g.5929G→A; g.6510 G→A]	TaqI−; Sau96I+		[E144K; A155T]	<1.0; 0.0	Present	2, 3
2	c.494 G→A	g.6541 G→A	BsoFI−		C165Y	1.3	ND	4
2	c.526 G→A	g.6573 G→A	BstXI+		E176K	0	Present	2
2	c.1226 G→A	g.13221 G→A	BslI−	NMD	W409X	∼200	Present	5
1	c.28_29delG	g.28_29delG	BslI−e		E9fs, 81X	ND	ND
1	c.194 A→G	g.194 A→G	MaeIII+		H65R	ND	ND
1	IVS1−1G→C	g.3576 G→C	BslI−e	c.210_235del26	A69fsX94	ND	ND
1	c.341 C→T	g.5840 C→T	MaeII+		A114V	0–54.5	Decreased/present	2, 6
1f	[IVS7+1 G→A; IVS11+39del99]	[g.8297 G→A; 13000_13098del99]	None	c.737_828del92,g NMD; c.828_931ins104,g NMD	D245fsX298g; R276fsX295g	ND	ND

Note.— ND = not determined.

^a− = mutation abolishes restriction site; + = mutation forms a novel restriction site.

^bNMD = nonsense-mediated decay.

^cCatalytic activity of mutant CBS in E. coli extracts, expressed as percent of wild-type CBS.

^dSources of protein information are as follows: 1, Kozich and Kraus 1992; 2, this study; 3, Dawson et al. 1997; 4, Kluijtmans et al. 1999; 5, Shan and Kruger 1998; and 6, de Franchis et al. 1994.

^eRestriction sites formed using mismatched PCR primer (see Primers and Conditions Web site).

^fAllele carrying two mutations in cis.

^gMutation IVS7+1G→A yields two mutant mRNA isoforms depending on the use of an alternative splice site; these isoforms are present only in the nuclear RNA preparation (data not shown).