We have sequenced a number of cDNAs representing the Bombyx mori silk fibroin heavy chain transcript. These reveal that the central region of the fibroin gene is composed of alternate arrays of the crystalline element a and the noncrystalline element b. The core region is partitioned by a homogeneous nonrepetitive amorphous domain of around 100 bp in length. The element a is characterized by repeats of a highly conserved 18-bp sequence coding for perfect repeats of the unit peptide Gly-Ala-Gly-Ala-Gly-Ser. The element b is composed of repeats of a less-conserved 30-bp sequence which codes for a peptide similar to that in element a except in that (1) Ser is replaced by Tyr and (2) there are irregular substitutions of Ala to Val or Tyr. Therefore, the structure of the fibroin gene core consists of three-step higher-order periodicities. Heterogeneities in numbers of repeats are observed in each step of periodicity. Boundary sequence appeared in each periodicity to be quite homogeneous. Sequence analysis indicates that the unit sequences of elements a and b have homology to those of recombination hotspots reported in other genes and a recombination event may frequently occur between the misaligned sister chromatids, resulting in heterogeneities in repeat numbers and duplication or deletion of repetitive sequences. The repetitive superstructure of the fibroin gene may have been a result of continuous unequal crossovers in a primordial gene during evolution. A couple of important features of the fibroin protein were proved by the present nucleotide sequencing.(ABSTRACT TRUNCATED AT 250 WORDS)

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Staphylococcus saprophyticus is a uropathogenic bacterium that causes acute uncomplicated urinary tract infections, particularly in female outpatients. We investigated the dissemination and antimicrobial susceptibilities of 101 S. saprophyticus isolates from the genitourinary tracts of patients in Japan. Eight of these isolates were mecA positive and showed ␤-lactam resistance. Pulsed-field gel electrophoresis showed that only some isolates were isogenic, indicating that the mecA gene was apparently acquired independently by mecA-positive isolates through staphylococcal cassette chromosome mec (SCCmec). Type determination of SCCmec by multiplex PCR showed a nontypeable element in the eight mecA-positive isolates. Sequence analysis of the entire SCCmec element from a prototype S. saprophyticus strain revealed that it was nontypeable with the current SCCmec classification due to the novel composition of the class A mec gene complex (IS431-mecAmecR1-mecI genes) and the ccrA1/ccrB3 gene complex. Intriguingly, the attachment sites of SCCmec are similar to those of type I SCCmec in S. aureus NCTC 10442. Furthermore, the genes around the mec gene complex are similar to those of type II/III SCCmec in S. aureus, while those around the ccr gene complex are similar to those of SCC15305RM found in S. saprophyticus ATCC 15305. In comparison with known SCCmec elements, this S. saprophyticus SCCmec is a novel type.Staphylococcus saprophyticus is a member of the coagulasenegative staphylococci (CoNS), which frequently cause uncomplicated urinary tract infections (UTIs) in young and middleaged female outpatients (8,12,15,18,21,22,23). Unlike most other CoNS, S. saprophyticus is rarely resistant to most antibiotics active against gram-positive organisms (10,17).Although the UTIs caused by S. saprophyticus have been well documented, the antimicrobial resistance and dissemination of this species are not well studied. The study described here investigated the current dissemination and antimicrobial resistance of S. saprophyticus isolates recovered from the urogenital tracts of Japanese patients. In addition, the characterization of a new type of staphylococcal cassette chromosome mec (SCCmec) element from a mecA-positive S. saprophyticus was carried out. MATERIALS AND METHODSBacterial isolates. From April to December 2003, a total of 101 S. saprophyticus isolates were recovered from urine specimens (94 isolates) of patients with acute cystitis with bacterial counts of Ն10 4 CFU/ml or vaginal specimens (7 isolates) of patients with from bacterial vaginosis-or candidiasis-related symptoms at the clinical microbiology laboratories of 65 different Japanese hospitals. All isolates were from different patients, and duplicate isolates from the same patient were excluded. In addition, specimens also yielding gram-negative bacteria, which are often isolated from patients with either uncomplicated or complicated UTIs, were not considered for further isolation of CoNS, including S. saprophyticus. These isolates were identified as CoNS by means...

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