Objective To study the relationship between erythromycin sensitivity and drug-resistance gene in Mycoplasma pneu-moniae(Mp).Methods In 46 erythromycin-resistant MP clinical isolates,domain Ⅴ of 23S rRNA was amplified by polymerase chain reaction(PCR),followed by direct automatic sequencing method.The DNA sequences were compared to find molecular mecha-nisms of drug resistance.Results Among the 46 erythromycin-resistant Mp clinical isolates,44(95.65%)harbored an A-to-G tran-sition mutation at position 2063 in the 23S rRNA gene and 2(4.35%)harbored an A-to-G transition mutation at position 2064,but no A-to-C transition mutation at position 2063 and C-to-G/A transition mutation at position 2617 were detected.Conclusion E-rythromycin-resistant of Mp clinical isolates were closely related to A-to-G transition mutation at position 2063/2064 in domain Ⅴof 23S rRNA genes and the most important was the A2063G transition mutation.Rapid and accurate identification of the genetic mutations in domain Ⅴ of 23S rRNA may be help to diagnose the infection of Mycoplasma pneumoniae,provide the drug-resistant information,and instruct the application of antibiotics reasonably and effectively.

Our recent investigation in the protist Trichomonas vaginalis suggested a DNA sequence periodicity with a unit length of 120.9 nt, which represents a sequence signature for nucleosome positioning. We now extended our observation in higher eukaryotes and identified a similar periodicity of 175 nt in length in Caenorhabditis elegans. In the process of defining the sequence compositional characteristics, we found that the 10.5-nt periodicity, the sequence signature of DNA double helix, may not be sufficient for cross-nucleosome positioning but provides essential guiding rails to facilitate positioning. We further dissected nucleosome-protected sequences and identified a strong positive purine (AG) gradient from the 5'-end to the 3'-end, and also learnt that the nucleosome-enriched regions are GC-rich as compared to the nucleosome-free sequences as purine content is positively correlated with GC content. Sequence characterization allowed us to develop a hidden Markov model (HMM) algorithm for decoding nucleosome positioning computationally, and based on a set of training data from the fifth chromosome of C. Elegans, our algorithm predicted 60%-70% of the well-positioned nucleosomes, which is 15%-20% higher than random positioning. We concluded that nucleosomes are not randomly positioned on DNA sequences and yet bind to different genome regions with variable stability, well-positioned nucleosomes leave sequence signatures on DNA, and statistical positioning of nucleosomes across genome can be decoded computationally based on these sequence signatures.

To enrich the genomic information of the commercially important fish species, we obtained 5,063 high-quality expressed sequence tags (ESTs) from the muscle cDNA database of the mandarin fish (Siniperca chuatsi). Clustering analysis yielded 1,625 unique sequences including 443 contigs (from 3,881 EST sequences) and 1,182 singletons. BLASTX searches showed that 959 unique sequences shared homology to proteins in the NCBI non-redundant database. A total of 740 unique sequences were functionally annotated using Gene Ontology. The 1,625 unique sequences were assigned to Kyoto Encyclopedia of Genes and Genomes reference pathways, and the results indicated that transcripts participating in nucleotide metabolism and amino acid metabolism are relatively abundant in S. chuatsi. Meanwhile, we identified 15 genes to be abundantly expressed in muscle of the mandarin fish. These genes are involved in muscle structural formation and regulation of muscle differentiation and development. The most remarkable gene in S. chuatsi is nuclease diphosphate kinase B, which is represented by 449EST sequences accounting for 8.86% of the total EST sequences. Our work provides a transcript profile expressed in the white muscle of the mandarin fish, laying down a foundation in better understanding of fish genomics.

Baylisascaris schroederi,a roundworm(ascaridoid)parasite specific to the bamboo-feeding giant panda(Ailuropoda melanoleuca),represents a leading cause of mortality in wild giant panda populations.Here,we present a 293-megabase chromosome-level genome assembly of B.schroederi to infer its biology,including host adaptations.Comparative genomics revealed an evolutionary trajectory accompanied by host-shift events in ascaridoid parasite lineages after host separations,suggesting their potential for transmission and rapid adaptation to new hosts.Genomic and anatomical lines of evidence,including expansion and positive selection of genes related to the cuticle and basal metabolisms,indicate that B.schroederi undergoes specific adaptations to survive in the sharp-edged bamboo-enriched gut of giant pandas by structurally increasing its cuticle thickness and efficiently utilizing host nutrients through gut parasitism.Additionally,we characterized the secretome of B.schroederi and predicted potential drug and vaccine targets for new control strategies.Overall,this genome resource provides new insights into the host adaptation of B.schroederi to the giant panda as well as the host-shift events in ascaridoid parasite lineages.Our findings on the unique biology of B.schroederi will also aid in the development of prevention and treatment measures to protect giant panda populations from roundworm parasitism.