The fluorescence of Y-bodies and brightly fluorescing autosomal heterochromatin in quinacrine mustard stained interphase nuclei treated with distamycin A is more brilliant than in nuclei stained only with quinacrine and mustard. In the present study examinations with the aid of this method in several probands and different tissues are described. The effect of distamycin A is demonstrated to depend on its dose and the time of exposure to it. An exceptionally high frequency of YY sperm nuclei, previously also described by other studies, is confirmed in the present work. A hypothesis explaining the effect of distamycin A in interphase nuclei is discussed.

Mismatch repair contributes to hypermutation in B lymphocytes, both by increasing the frequency of mutations and by changing the mutational patterns. In this paper, we investigated whether or not mismatch repair influences activation-induced cytidine deaminase (AID)-mediated hypermutation in a non-B lymphocyte line. We did so by regulating expression of MutL homologue MLH 1, which is essential in mismatch repair, in a kidney cell line that had been transduced by an AID-containing vector. Whether or not MLH1 was expressed, we found no difference in the mutation rates of an indicator gene. We conclude that in order to contribute to hypermutation, mismatch repair needs additional factors that are present in activated B lymphocytes, but absent in the cell line investigated. IntroductionSomatic hypermutation contributes to antibody diversity through introduction of point mutations into the variable (V) region of immunoglobulin sequences [1]. The mutation rate in mice and humans is about 10 6 -fold higher than the spontaneous mutation rate in most other genes [2]. Targeting of somatic hypermutation to the Ig loci remains a subject of debate, since genomic sites other than the Ig loci have been reported to support hypermutation to various degrees [3][4][5][6]. However, somatic hypermutation is triggered by and restricted to the expression of the activation-induced cytidine deaminase (AID) enzyme in activated germinal center B cells [7][8][9][10]. Ectopic expression of AID in hybridomas [11], non-B cells [12,13] and even E. coli [14] results in a mutator phenotype. In conjunction with replication protein A (RPA) [15], AID acts on single-stranded DNA during transcription and deaminates dC into dU [16][17][18]. If the mismatch is not repaired, it results in a C?T transition, which is the predominant mutation during ectopic AID expression in cell lines and E. coli. After introduction of the G-U mismatch, various pathways fix the mutation in the genome (reviewed in [19]). For example, the uracil N-glycosylase (UNG) removes the uracil generated by AID [20]. If the resulting abasic site is converted by an AP-endonuclease into a singlestrand nick and subsequently repaired via the base excision pathway, no mutation is generated. But if the abasic site is not removed, any base can be introduced during replication [21]. Alternatively, although debated [22], mismatch repair (MMR) may sense G-U mispairing and set off a sequence of events that introduces further mutations rather than restore the original base pair sequence [23] (reviewed in [24] [39]. Cancer predisposition is linked to germ-line mutations in MMR genes; most mutations associated with HNPCC were found in hMLH1, hMSH2, and hMSH6 genes [40], while mutations in hPMS2 were reported sporadically. The majority of all HNPCC-causing mutations were found in hMLH1, focusing the interest on the analysis of pathogenic hMLH1 variants [41]. Although loss of EXO1, FEN1 and PCNA function also results in a mutator phenotype, it does not seem to significantly contribute to HNPCC forma...

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Codon Red Identification and optimization of fluorescent proteins, coupled with advances in imaging technology, have been a boon to the analysis of gene expression in vivo and in vitro. Of available fluorescent proteins, one of the most widely used is DsRed2, originally cloned from a coral of the Discosoma genus. Klasen and Wabl (p. 236) describe the introduction of a silent point mutation in the DsRed2 gene, which, when the gene is expressed in mammalian cells, results in a significant increase in relative fluorescence over that produced by the product of the unmutated gene alone. The modification entails conversion of cytodine to adenosine at nucleotide position 537 (hence the moniker DsRed 537) and results in the conversion of serine codon UCC at this site to serine codon UCA. The observed improvement in fluorescence is likely due, at least in part, to utilization of a previously unavailable tRNA pool recruited by codon UCA but not by UCC. Regardless of the underlying mechanism, these observations may influence codon optimization strategies, and DsRed 537 constitutes a new tool for use in multicolor tagging.

The proband was born when the mother was 27 and the father 32 after a normal pregnancy and delivery. The parents and an older brother are healthy with normal karyotypes. At 13j years she had severe mental and physical retardation, general muscular hypotonia, hyperactivity, and trichotillomania. Height and weight were below the 3rd centile, ossification was delayed, and she had brachycephaly, a wide fontanelle, deep-seated ears, hypertelorism, and antimongoloid slants. Bilateral cleft lip and palate had been treated surgically. Hands and feet were short, Dubois sign was positive, there was bilateral clinodactyly, and syndactyly between fingers 2 and 3, and more markedly between toes 2, 3, and 4. There were single transverse palmar creases on both hands and diastasis of the rectus abdominis muscle. X-ray examination showed asymmetry of the os sacrum and spina bifida occulta. Chronic constipation, gastrooesophageal reflux, and disturbed micturition were reported. The external genitalia were normal, no testes were palpable, and there was no onset of puberty.G banding of the proband's lymphocytes revealed an aberrant chromosome 9 which is interpreted as an inverted tandem ('mirror') duplication of 9p (figure a). Of 100 metaphases investigated, 97 showed, in addition to a single X chromosome, a small acrocentric chromosome which was identified as a Y by Q and C banding and distamycin A pretreatment' (figure b, d). Presence of Y heterochromatin specific repeated sequences was confirmed by Hae III restriction endonuclease analysis of the DNA of the proband, father, and brother. The remaining three metaphases lacked a Y chromosome. After staining preparations of the proband with quinReceived for publication 9 March 1981 Short reports acrine mustard, C banding showed an extremely large block of constitutive heterochromatin in one chromosome 7 (figure c). This particular chromosome was also seen in the mother and brother. Using a cytotoxicity assay technique, the proband was found to be negative for the H-Y antigen.The karyotype of the proband is therefore 45,XO,inv dup(9)(pter-p24 p21 p24 p21 -qter)/46,XY,inv dup(9)(pter --p24 p21 -)p24 p21 --qter). Trisomy 9p could not be confirmed by gene dosage measurements (eg galactose-1-P-uridyl transferase), nor could the internal genitalia be explored, since the proband's parents refused any further examination. However, the phenotype of the proband clearly shares features with previously reported cases of XY gonadal dysgenesis2 and trisomy 9p.