Quantitative and qualitative comparisons of spontaneous and radiation-induced specific-locus mutation in the ad-3 region of heterokaryon 12 of Neurospora crassa

The data from forward-mutation experiments to obtain specific-locus mutations at two closely linked loci in the adenine-3 (ad-3) region of heterokaryon 12 (H-12) of Neurospora crassa have been used to determine the relative frequencies and mutational spectra of ad-3 mutants occurring spontaneously and those induced by 7 different radiation treatments. Previous studies have demonstrated that specific-locus mutants at these two loci result from 5 major genotypic classes, namely two classes of gene/point mutations (ad-3AR and ad-3BR), and 3 classes of multilocus deletion mutations ([ad-3A]IR, [ad-3B]IR and [ad-3A ad-3B]IR). Two different approaches were used to compare spontaneous mutation in the ad-3 region with that induced by 7 different radiation treatments (UV, 32P, 447 MeV protons, 85Sr, 250 kVp X-rays, 39 MeV helium ions, and 101 MeV carbon ions). These comparisons included X2-tests on the numbers of ad-3 mutants resulting in the following two sets of ratios: (1) gene/point mutations and multilocus deletion mutations; and (2) complementing and non-complementing ad-3BR mutants. Combination of the data from these two methods of comparison has demonstrated that each of the 7 radiation treatments induced a spectrum of ad-3 mutants that is statistically different from the spontaneous spectrum. In addition, these same two methods of comparison have been used to compare the mutagenic effects of each of the 7 radiation treatments with each other. Combination of the data from these two methods of comparison demonstrated that the majority of radiation-induced specific-locus mutations: (90.5% (19/21 of the pairwise combinations)) are qualitatively different from each other. We conclude that the mechanisms by which various radiations modify DNA tend to exhibit fundamental differences from each other and from the processes involved in spontaneous mutation.

Quantitative and qualitative aspects of spontaneous specific-locus mutation in the ad-3 region of heterokaryon 12 of Neurospora crassa

The data from forward-mutation experiments to obtain specific-locus mutations at 2 closely linked loci in the adenine-3 (ad-3) region of heterokaryon 12 (H-12) of Neurospora crassa have been tabulated to determine the frequency of spontaneous ad-3 mutations and to determine the percentages resulting from each of the 2 major genotypic classes: gene/point mutations and multilocus deletion mutations. Gene/point mutations at the ad-3B locus (ad-3BR) have been characterized to determine the percentage showing allelic complementation to obtain a presumptive identification of the genetic alteration in each mutation at the molecular level. Data from experiments performed at 2 different laboratories have been compared to assess the interlaboratory reproducibility of quantitative data on H-12. No difference was found between the frequencies of spontaneous specific-locus mutations in the ad-3 region. Genetic analysis of 172 ad-3 mutants demonstrated that specific-locus mutations in the ad-3 region result from both gene/point mutations (82.0% [141/172]), and multilocus deletion mutations (14.5% [25/172]). Heterokaryon tests for allelic complementation demonstrated that 52.5% (53/101) spontaneous ad-3BR mutants show allelic complementation, and result from single base-pair alterations. In addition, 100% (25/25) of the spontaneous multilocus deletion mutations result from the 3 smallest sized genotypic subclasses. The implications of the present experimental data for the validation of the ad-3 specific-locus assay system in Neurospora are discussed.

Hb Adana or alpha 2(59)(E8)Gly-->Asp beta 2, a severely unstable alpha 1-globin variant, observed in combination with the -(alpha)20.5 Kb alpha-thal-1 deletion in two Turkish patients

We have identified a severely unstable hemoglobin variant through sequencing of amplified DNA involving the alpha 1-globin gene; the mutation is located in codon 59 (CCG CAG) and results in a Gly-->Asp replacement. This amino acid substitution concerns a glycine residue at an internal position in the E helix, which is in close contact with a glycine residue of the B helix; introduction of the larger and charged aspartic acid residue greatly affects the stability of the molecule. This variant was present in association with a common alpha-thalassemia-1 deletion [-(alpha)20.5 kb] in two adults and caused a severe type of Hb H disease with anemia, low levels of Hb A2, increased zeta chain, and Hb Bart's. In vitro chain synthesis in reticulocytes showed a high specific activity of the variant alpha chain. Only a minute quantity of Hb H was present but instead about 10% of Hb Bart's was observed. The increased synthesis of gamma chains was likely due to specific characteristics of a chromosome with haplotype #3, which was present in both patients. The same family was studied 18 years ago; the improved methodology presently available has led to a corrected diagnosis for these patients.

Hb Sinai-Baltimore or alpha 2 beta (2)18(A15)Val->Gly, a silent, mildly unstable beta chain variant detected by isoelectrofocusing and high performance liquid chromatography

Isoelectrofocusing and high performance liquid chromatographic methods were used to study an abnormal hemoglobin present in a Black male infant and his mother. The variant, named Hb Sinai-Baltimore, focused slightly behind Hb A and separated incompletely from Hb A by cation exchange high performance liquid chromatography, while the separation of the beta A and beta X chains by reversed phase high performance liquid chromatography was complete. The variant was identified through an analysis of peptides in a tryptic digest of the isolated beta X chain and by sequencing of amplified DNA which included the beta-globin gene. The Val->Gly replacement at position beta 18 (codon 18; GTG->GGG) or at the last position of the A helix decreases the stability of the variant without affecting the hematological parameters of its carrier. The propositus was a compound heterozygote for Hb Sinai-Baltimore and Hb S; the relative quantities of the two variant chains were somewhat different from those of the beta X and beta A chains in the mother with the simple Hb Sinai-Baltimore heterozygosity. An uncertainty about the alpha-globin gene status in the child prevented a further evaluation of these differences.

Heterogeneity of the hemoglobin of the Ohrid trout (Salmo L. typicus)

We have analyzed the hemoglobins of five individual trout from the Ohrid Lake (Salmo L. typicus) by electrophoretic methods, by reversed-phase high-performance liquid chromatography, and by limited structural analyses. The two major classes of hemoglobin are type I (35% of total) and type IV (65%). Type IV is the major oxygen-transporting hemoglobin; it consists of three types of beta chain (in about equal quantities) and three types of alpha chain (one major and two minor types). Several structural differences have been observed between these three beta (IV) chains and between the three alpha (IV) chains, suggesting a complex genetic system governing the synthesis of these proteins. Moreover, a few amino acid substitutions occur at positions involved in contacts between chains, which suggests that differences in oxygen affinity may exist between these various type IV hemoglobins. Type I hemoglobin is less complex because it contains one type of beta chain and two alpha chains; the latter two differ in numerous positions, suggesting duplications of the alpha (I)-globin gene. The alpha and beta chains of type I hemoglobin differ considerably from the alpha and beta chains of type IV hemoglobin, indicating the existence of alpha (I)- and beta (I)-globin genes separate from the alpha (IV)- and beta (IV)-globin genes.

The linkage of Hb Valletta [alpha 2 beta 287(f3)Thr----Pro] and Hb F-Malta-I [alpha 2G gamma 2117(G19)His----Arg] in the Maltese population

We have identified a new stable abnormal hemoglobin called Hb Valletta, which is characterized by a Thr----Pro substitution at position 87 of the beta chain. This mutation was found to be linked to that of the gamma chain variant Hb F-Malta-I with a His----Arg mutation at position 117 of the G gamma chain. Both variants were detected in the blood samples of 34 Maltese and two Italian newborn babies with isoelectrofocusing and reversed phase high performance liquid chromatography. Similar analyses of cord blood from 388 additional Maltese newborns failed to identify either one of these two variants. Additional analyses of 353 Maltese adults (including 39 beta-thalassemia heterozygotes) resulted in the detection of two adult Hb Valletta heterozygotes. Dot-blot hybridization analyses of amplified DNA with a probe specific for the G gamma-F-Malta-I variant showed that both also carried that mutation. These results show close linkage of the mutant forms of the G gamma- and beta-globin genes, 27-28 kb apart, and a failure to identify chromosomes with either the Hb F-Malta-I mutation alone or with the Hb Valletta mutation alone, indicating a low recombination frequency.

Hb Cleveland or alpha 2 beta 2(93)(F9)Cys----Arg;121(GH4)Glu----Gln

Hb Cleveland is characterized by two amino acid substitutions, namely beta 121(GH4)Glu----Gln as in Hb D-Los Angeles and beta 93(F9)Cys----Arg as in Hb Okazaki, and shares with Hb Okazaki a decreased stability, an increase in oxygen affinity, and decreases in Bohr effect and heme-heme interaction. It is the 13th beta chain variant with two substitutions that has been described thus far.

Hemoglobin Montreal: a new variant with an extended beta chain due to a deletion of Asp, Gly, Leu at positions 73, 74, and 75, and an insertion of Ala, Arg, Cys, Gln at the same location

The unstable hemoglobin Montreal with a deletion of three amino acid residues (Asp, Gly, Leu) at positions 73, 74, and 75 of the beta chain and an insertion of four residues (Ala, Arg, Cys, Gln) at the same location was observed in a 7-year-old Canadian boy suffering from a moderate hemolytic anemia. The introduction of an extra amino acid residue and of other changes in the crevice where the heme group is located is the likely cause of the instability of this hemoglobin variant. The above listed changes were detected through analyses of tryptic peptides of the beta-Montreal chain, sequencing of amplified DNA, and hybridization of amplified DNA with appropriate, 32P-labeled, oligonucleotide probes. It is suggested that a mispairing involving the AGTG sequences at codons 66 and 67 and at codons 72 and 73 of the normal beta gene caused a repetition of a 16-bp segment, while a deletion of 10 nucleotides due to recombination or slippage followed by a second short deletion during DNA repair resulted in the modified sequence of the beta-Montreal gene.

Hemoglobin Birmingham and hemoglobin Galicia: two unstable beta chain variants characterized by small deletions and insertions

Two unstable hemoglobins (Hbs) causing rather severe hemolytic anemia have been characterized. The beta chain of Hb Birmingham, found in an adult black man, is characterized by the loss of -Leu-Ala-His-Lys- at positions 141, 142, 143, and 144 and their replacement by one Gln residue. These changes are the result of a deletion of nine nucleotides, namely two base pairs (bp) of codon 141, all of codons 142 and 143, and one bp of codon 144; the remaining CAG triplet (C from codon 141 and AG from codon 144) codes for the inserted glutamine. In the beta chain of Hb Galicia from a Spanish patient, His and Val at positions 97 and 98 are replaced by one Leu residue. This is due to an ACG deletion in codons 97 and 98, which causes the removal of one His and one Val residue, while the remaining CTG triplet (C from codon 97 and TG from codon 98) codes for the inserted leucine residue. Two mechanisms, namely slipped mispairing in the presence of short repeats, and misreading by DNA polymerase due to a local distortion of the DNA helix, are considered in explaining the origin of the small deletions.

Hb Sun Prairie or alpha(2)130(H13)Ala----Pro beta 2, a new unstable variant occurring in low quantities

A severe hemolytic anemia with microcytosis and hypochromia was present in a young adopted Indian patient. Reversed phase high performance liquid chromatographic methodology and heat stability tests detected an unstable alpha chain which was present in 3 to 5% of the total hemoglobin. A larger quantity of the alpha X chain was obtained by preparative reversed phase high performance liquid chromatography. Structural analyses identified an Ala----Pro replacement at position 130 of the alpha chain. The instability of the variant, named Hb Sun Prairie, is comparable to that of Hb Bibba [alpha 136 (H19)Leu----Pro]. Gene mapping failed to detect an alpha-thalassemia deletion (alpha alpha/alpha alpha), while dot-blot analysis of amplified DNA with synthetic probes localized a G----C mutation in codon 130 (resulting in the Ala----Pro mutation) of the alpha 2-globin genes of both chromosomes. These results suggest a homozygosity for the G----C mutation and the condition alpha 2(G----C)alpha 1/alpha 2(G----C)alpha 1 adequately explains the rather severe clinical status of this child, including the marked microcytosis and hypochromia. Unfortunately, family studies to exclude the presence of a large deletion involving all zeta- and alpha-globin genes were not possible.

Hb Davenport or alpha 2(78)(EF7)Asn----His beta 2

Hb Davenport is a new, stable alpha chain variant, that was detected in two members of a Caucasian family living in Iowa. Hematological data were within normal limits. It is characterized by an Asn----His replacement at position alpha 78. Mild acidic hydrolysis of the large alpha T-9 peptide, separation of the resulting fragments by reversed phase high performance liquid chromatography, and sequence analysis of a few of these peptides greatly facilitated the identification of this substitution.

Hb F-Jiangsu, the first gamma chain variant with a valine----methionine substitution: alpha 2A gamma 2 134(H12)Val----Met

During a survey of cord blood samples of healthy Chinese babies an A gamma variant was detected by its partial separation from normal A gamma in a high performance liquid chromatographic experiment. Structural analysis of the isolated A gamma X chain identified a Val----Met substitution at position A gamma 134; this substitution created a rather unique Met-Met sequence. The ratio of A gamma X to A gamma was about 2 to 3; thus, Hb F with this variant A gamma chain appears to have approximately normal stability.

Hb Hekinan observed in three Chinese from Macau; identification of the GAG----GAT mutation in the alpha 1-globin gene

Hb Hekinan, an alpha chain variant that is characterized by a Glu----Asp mutation at position alpha 27, was observed in three Chinese females attending a prenatal clinic in Macau. The relative quantities of the stable hemoglobin were 13-14% (average 13.3%); its identification was greatly aided by the separation and purification of the peptides by reversed phase high performance liquid chromatography. Dot-blot analysis of amplified DNA with 32P-labeled probes located the mutation in codon 27 of the minor alpha 1-globin gene; the change involved a GAG (coding for glutamic acid) to GAT (coding for aspartic acid) mutation.

Hb Chad or alpha 223(B4)Glu----Lys beta 2 observed in members of a Surinam family in association with alpha-thalassemia-2 and with Hb S

Three different hemoglobinopathies, i.e. Hb S, Hb Chad [alpha 23 (B4)Glu----Lys], and alpha-thalassemia-2 (-3.7) have been observed in eight members of a family from Surinam. The proposita had all three abnormalities, while her mother and four of her half-brothers had Hb Chad together with an alpha-thalassemia-2 heterozygosity or homozygosity. Gene mapping and dot-blot analysis of amplified DNA identified a G----A mutation in codon 23 of the alpha 2 alpha 1 hybrid gene resulting in the Glu----Lys substitution. The quantity of the alpha-Chad chain averaged 31.5% in its carriers with an additional alpha-thalassemia-2 heterozygosity [-alpha Chad(-3.7 kb)/alpha alpha], and 43% in the two carriers with an additional alpha-thalassemia-2 homozygosity [-alpha Chad (-3.7 kb)/-alpha (3.7 kb)]. These quantities are considerably higher than those reported for families from Chad, China, and Japan; the low levels of 14.5-24% Hb Chad in members of previously reported cases suggest a mutation on a chromosome with two alpha-globin genes [alpha alpha Chad/alpha alpha or alpha Chad alpha/alpha alpha].

Hb Evans or alpha 262(E11)Val----Met beta 2; an unstable hemoglobin causing a mild hemolytic anemia

Structural analysis of the alpha chain of the hemoglobin from a Caucasian female with a mild hemolytic anemia showed the presence of a variant with a Val----Met substitution at position alpha 62. The valine at this position forms one of the contacts with heme and its replacement by methionine will likely decrease heme binding and cause a distortion of the heme crevice and a decreased stability of the abnormal protein. Dot-blot analysis of amplified DNA with 32P-labeled synthetic oligonucleotide probes confirmed the suspected G----A mutation in the first position of codon 62, and also located the mutation in the alpha 2-globin gene. The mutation was found in the proposita and one of her daughters but was most probably absent in her parents.

Hb natal or alpha 2(minus Tyr-Arg) beta 2: a high oxygen affinity alpha chain variant with a deleted carboxy-terminus resulting from a TAC----TAA (Tyr----terminating codon) mutation in codon alpha 140

The discovery is reported of a fast-moving alpha chain variant (Hb Natal) which is characterized by a shortened alpha polypeptide chain because of the deletion of the Tyr-Arg carboxy-terminal residues. Through amplification of appropriate segments of DNA and hybridization with synthetic oligonucleotide probes, it was possible to detect a C----A mutation in codon 140 of the alpha 2 globin gene, which causes a change in the codon for tyrosine to a terminating codon. Hb Natal or alpha 2 (minus Tyr-Arg) beta 2 has a high affinity for oxygen without a Bohr effect and heme-heme interaction. These results provide direct evidence for the importance of the tyrosine residue at alpha 140 in the oxygenation-deoxygenation process.

Some rare hemoglobin variants with altered oxygen affinities; Hb linkoping [beta 36(C2)Pro----Thr], Hb Caribbean [beta 91(F7)Leu----Arg], and Hb Sunnybrook [beta 36(C2)Pro----Arg]

A few rare hemoglobin variants with altered functional properties have been observed in Canadian subjects with either an erythrocytosis or mild anemia. These variants were Hb Alberta [beta 101(G3)Glu----Gly], Hb Linkoping [beta 36(C2)Pro----Thr], a new variant Hb Sunnybrook [beta 36(C2)Pro----Arg], and Hb Caribbean [beta 91(F7)Leu----Arg]. Short clinical descriptions of the subjects are given, the characterization of the variants is described in detail (except for Hb Alberta), while data from some functional analyses are provided. Comparisons with previously published data have been made and the unusual chromatographic property of two abnormal beta chains in a reversed phase high performance liquid chromatographic system is reviewed.

Hb Las Palmas or alpha 2 beta 2(49)(CD8)Ser----Phe, a mildly unstable hemoglobin variant

A new hemoglobin variant with a Ser----Phe substitution at position beta 49(CD8) was discovered in two members of a family living in the Canary Islands, Spain. Detection was by polyacrylamide gel electrophoresis and by reversed phase high performance liquid chromatography. The variant, which constituted 43% and 45%, respectively, in the two heterozygotes, was slightly unstable. Its presence did not affect hematological values though there was a mild reticulocytosis.

Hb Duan [alpha 75(EF4)Asp----Ala], Hb Westmead [alpha 122(H5)His----Gln], and alpha-thalassemia-2 (-4.2 Kb deletion) in a Chinese family

Detailed data are presented concerning the relative amounts of Hb A and two alpha chain variants (Hb Duan with alpha 75 Asp----Ala, and Hb Westmead with alpha 122 His----Gln), and the occurrence of an alpha-thalassemia-2 heterozygosity in five members of a small Chinese family. The three children who have the three abnormalities inherited the alpha-Duan and alpha-thalassemia-2 heterozygosities from their father, and the alpha-Westmead heterozygosity from their mother. The base substitution which leads to the synthesis of the alpha-Duan chain occurred at codon 75 of the alpha 1 globin gene of the chromosome which also carried the alpha-thalassemia-2 deletion; the concentration of alpha-Duan (37% of total alpha) is similar to that observed for other alpha chain variants, linked to an alpha-thalassemia-2 condition.

Hb J-Antakya or alpha 2 beta (2)65(E9)Lys----Met in a Turkish family and Hb complutense or alpha 2 beta (2)127(H5)Gln----Glu in a Spanish family; correction of a previously published identification

Almost 10 years ago we reported in this journal the characterization of Hb Hacettepe or alpha 2 beta (2)127(H5)Gln----Glu. Unfortunately, we have to conclude that the original characterization of this Turkish variant was in error. The corrected data are presented in this short communication. The variant (alpha 2 beta (2)65(E9)Lys----Met) was (re)named Hb J-Antakya, after the city where the family resides. An abnormal Hb, observed in a Spanish family and named Hb Complutense, had the beta 127 Gln----Glu substitution, erroneously assigned to the Turkish variant.

HB Chicago or alpha (2)136 (H19) Leu----Met beta 2 and a -G gamma-G gamma-globin gene arrangement in a black family

Hb Chicago is a newly discovered hemoglobin variant which was present in a Black newborn baby and her father. The leucine residue at alpha 136, which normally participates in the contact with the heme group, is replaced by a methionine residue. The two heterozygotes were clinically well with normal hematological data. Isolation of the alpha X and alpha A chains by reverse phase high performance liquid chromatography and hydrolysis of these chains with dilute formic acid at 110 degrees C for 24 hours, followed by separation of the resulting peptides by reverse phase high performance liquid chromatography, greatly facilitated the final identification of the abnormality. The baby and both parents had a -G gamma-G gamma-globin gene arrangement on one chromosome (normal: -G gamma-A gamma-) which explains the high G gamma values in the Hb F of these three persons.

The identification of five rare beta-chain abnormal hemoglobins by high performance liquid chromatographic procedures

The detection, quantitation, and characterization of five relatively rare beta chain abnormal hemoglobins mainly by high performance liquid chromatographic procedures are described. The variants involved are Hb City of Hope (beta 69 Gly----Ser), Hb Austin (beta 40 Arg----Ser), Hb Leiden (beta 6 or 7 Glu----0), Hb Louisville (beta 42 Phe----Leu), and Hb Presbyterian (beta 108 Asn----Lys). Some clinical and hematological data are also included.