SARS Virus Genomic Sequencing Raises Vaccine Hopes

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Last updated at: (Beijing Time) Monday, May 05, 2003

SARS Virus Genomic Sequencing Raises Vaccine Hopes

Chinese scientists have finished complete genomic sequencing of another isolate of a virus that is associated with severe acute respiratory syndrome (SARS).

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Chinese scientists have finished complete genomic sequencing of another isolate of a virus that is associated with severe acute respiratory syndrome (SARS).

A collaborative effort by scientists at the Institute of Microbiology and Epidemiology, Chinese Academy of Military Medical Sciences and the Beijing Genomics Institute (BGI), Chinese Academy of Sciences resulted in a comprehensive paper published on Saturday on the Internet edition of the Chinese Science Bulletin.

By comparing the complete sequence of the Isolate BJ01 they produced and those of four other isolates identified in the United States, Canada and Hong Kong, scientists are able to get closer to "the real killers" in the SARS-associated virus, said Yang Huanming, director of the BGI and one of the co-authors.

The research conducted so far shows the SARS-associated virus is very new -- unlike all other known viruses.

"The genome sequence of the SARS-associated virus provides essential information for scientists to identify pathogen(s) and interpret transmission and pathogenesis,'' Yang said.

The work will also pave the way for scientists to develop diagnostic tools and drugs for SARS and work out preventive measures such as future vaccines, Yang said.

He and his colleagues found the whole genome of SARS virus is composed of a stable protein -- RNA-dependent polymerase -- which accounts for two-thirds of the genome sequence and some variable proteins. Results of sequencing show that two of the variable proteins -- spike protein (S protein) and membrane protein (M protein) -- have a high mutation rate.

"It is these two kinds of proteins that help the SARS virus enter human cells, and then cause trouble,'' said Yang.

The comparative analysis indicates there are 31 substitutions among the variable proteins of the five complete genomes. Of the 31, nine can be found in two or three independent isolates of the SARS virus.

"This shows that SARS virus has strong variability,'' said Yang. "This will make it very difficult to produce SARS vaccines."

Phylogenetic studies show the genome of Isolate BJ01 is similar to one of the isolates identified in Hong Kong.

However, another isolate identified in Hong Kong might be closer to that from Toronto. The Toronto patient, from whom the isolate was obtained, travelled from Hong Kong, Yang said.

The isolate from the United States appears to be the farthest from all others.

Yang and his colleagues have also compared the SARS virus with 17 kinds of coronaviruses from both human beings and animals. These include four isolates from human beings, four from birds, two from rodents, and seven from house animals or pets.

"But there is no evidence yet that the SARS virus is linked with any of these viruses,'' he said.

BGI is currently trying to produce complete sequences of 10 isolates of the SARS virus. The already completed genome sequence of Isolate BJ01 was obtained from the lung of a dead SARS patient in Beijing. These isolates of the SARS virus were all provided by the Chinese Academy of Military Medical Sciences.

Yang said BGI has also completed draft sequences of another three isolates of the SARS virus from Beijing and an isolate of the SARS virus from Guangzhou.

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