Antibody EM48 and its reaction with N-terminal fragments of huntingtin. A, Schematic structure showing a truncated human huntingtin cDNA generated by PCR. Its corresponding region in wild-type huntingtin cDNA is shown above. The truncated protein contains only two glutamines in the glutamine repeat region and deletes the polyproline stretches. The numbers in parentheses represent the number of glutamines (Q) or prolines in normal human huntingtin.B, Western blots showing that EM48 recognizes native huntingtin (350 kDa band) in human brain cortex. C, EM48 immunofluorescent staining of 293 cells transfected with a series of cDNA constructs encoding different N-terminal fragments of human huntingtin with 120 glutamine repeats. The numbers in parentheses are N-terminal amino acid residues not including glutamine repeats. Note that only the huntingtin fragment (1–311) forms aggregates.