OBJECTIVE: To explore the molecular spectra and mechanism of human hypoxanthine 
guanine phosphoribosyl transferase (HPRT) gene mutation induced by 
ethyluitrosourea (ENU).
METHODS: Single cell cloning culture, two-way screening, multiple PCR 
amplification and electrophoresis technique were used.
RESULTS: With dose of ENU increasing, cell plating efficiency reduced (in the 
group with 100-200 micro g/ml doses, P < 0.01) and mutation frequency increased 
(in the group with 12.5-200.0 micro g/ml doses, P < 0.05) significantly. There 
was no all exons deletion in spontaneous mutations, and only 7.7% of them were 
detected as single exon deletion. But, deletion was found in 79.7% of 
ENU-induced mutations (62.5%-89.4%, P < 0.01), and deletion mutations in all 
nine exons of HPRT gene. Most of ENU-induced mutations were chain deletion with 
multiple exons (88.1%).
CONCLUSIONS: The spectra in spontaneous mutations differed completely from 
ENU-induced ones. ENU was liable to cause bigger changes in genetic structure, 
which suggested a stronger ENU's mutagenesis.