The HU protein isolated from Escherichia coli, composed of two partially homologous subunits, ot and 0, shares some of the properties of eucaryotic histones and is a major constituent of the bacterial nucleoid. We report here the construction of double mutants totally lacking both subunits of HU protein. These mutants exhibited poor growth and a pertubation of cell division, resulting in the formation of anucleate cells. In the absence of HU, phage Mu was unable to grow, to lysogenize, or to carry out transposition.The Escherichia coli HU protein is the most abundant DNA-binding protein present in the bacterial cell (38). This small, basic, dimeric protein interacts with double-stranded DNA, single-stranded DNA, and RNA. As with mixtures of the four core eucaryotic histones, HU can introduce negative supercoils into a relaxed closed circular DNA in vitro if topoisomerase I is present, and the resulting condensed structures resemble nucleosomes (5, 40). In addition, just as the histones in eucaryotes are conserved, the HU protein is highly conserved among procaryotic organisms and also in mitochondria and chloroplasts (10). It was shown earlier that HU is associated with the E. coli nucleoid (37, 47) (although some cytological observations were interpreted as locating HU on the edge rather than inside of the nucleoid [11]), but whether it has a role in maintaining the structure of the chromosome as a whole is not known.Biochemical studies have suggested a role for HU in the site-specific recognition of nucleotide sequences by other proteins (for a review, see reference 10). Among these interactions are the formation of protein-DNA complexes involved in the initiation of replication of the bacterial chromosome at oriC, in the hin-mediated gene inversion, and in the transposition of transposon TnJO and bacteriophage Mu. More precisely, replication from oriC (9, 13) and the transposition of TnJO (29,34) are moderately stimulated by HU protein, whereas the flagellar phase variation in Salmonella typhimurium (21) MATERIALS AND METHODSStrains and bacteria. The bacterial strains, plasmids, and phages used in this study are listed in Table 1. Bacteria were grown in LB (10 g of Bactotryptone [Difco Laboratories], 5 g of yeast extract, and 5 g of NaCl per liter) and counted on L agar (LA) (28). Minimal medium was M9 supplemented with thiamine (10 ,ug/ml), amino acids (100 pg/ml) or casamino acids (0.4%, wt/vol), and 0.4% (wt/vol) sugar (glycerol, maltose, lactose, or glucose). Kanamycin (25 p.g/ml), chloramphenicol (12.5 pLg/ml), streptomycin (200 pig/ml), and spectinomycin (100 ,ug/ml) were included when appropriate.Methods for Mu assays. The general methods used to manipulate the phage have been described previously (6,12 (ii) Mu transposition assay. The frequency of transposition onto the pUZ8 plasmid was measured by a mating-out assay. The Mu cts62pApl lysogens (or the bacteria infected with the bacteriophage X mini-Mu Apr) carrying pUZ8 were mated with the MFG625B recipient on a filter. After incubation for 2 h at 42...

Methylenetetrahydrofolate reductase (MTHFR) enzyme deficiency is the most common genetic cause of elevated levels of homocysteine in the plasma (hyperhomocysteinemia). We describe a 22‐year‐old male, who presented to the clinic with history of MTHFR deficiency and homocystinuria. At baseline, the patient was nonverbal, wheelchair‐bound with seizures since young age. Physical examination showed increased spasticity and weakness in bilateral lower extremities. Elevated levels of homocysteine were seen in the serum. Genetic testing revealed a single homozygous pathogenic mutation in c.1699C>T p. R587x. not previously reported for homocystinuria. Our patient carries a unique single homozygous pathogenic mutation c.1699C>T p. R587x leading to homocystinuria that hasn't been described before. More research is required to identify the pathophysiology of this mutation and role in other diseases.