BIOLOGY OF NON-A, NON-B HEPATITIS AGENTS

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Michael Houghton and colleagues at Chiron Corporation have cloned, expressed and sequenced at least part of the genome of the NANBH agent. They believe it is a 10KB, positive sense polyadenylated RNA virus that may be related to the alpha togaviruses. Sequence homology has not been found between the NANBH partial sequence and any other known viral sequence. I plan to use a variety of cDNA cloning procedures in order to confirm the Chiron findings. However, since they started with liter quantities of plasma that contained 106 infectious viruses/ml and I have approximately 100 ml of plasma of the same titer, the task is likely to be very difficult. It is hoped that the polymerase chain reaction technique will aid this effort. Molecular approaches to identifying the non-A, non-B hepatitis agent now involve development of technology that can be used to clone extremely small quantities of nucleic acid. We know that the NANBH agent is present in serum and even liver at very low levels, i.e., less than 106 infectious units per ml of serum or gram of liver. It also seems that if poly(A)+NANBH mRNA is produced, it is a very low abundance message. Therefore, either direct cloning of DNA or cDNA cloning is technically very difficult. In order to assist cloning small quantities of DNA or cDNA, a "nonclonable" piece of RNA or DNA has been produced. This non-clonable fragment will be added to NANBH nucleic acid preparations to act as a carrier for all cloning steps. This non-clonable fragment will be useful for a number of different cloning strategies where the level of the nucleic acid of interest is very low.