The G55R mutation increases the ability of 4R tau but not 3R tau to nucleate microtubule assembly.

<p>(A) Microtubule assembly in reactions containing a 1∶30 tau:tubulin dimer molar ratio were assayed by light scattering as a function of time. (B) Co-sedimentation assays demonstrate that the G55R mutation does not affect the ability of tau to assemble MT mass at steady-state, nor does it affect the ability of tau to bind to microtubules. Statistical significance was determined by comparing each mutant to its corresponding WT using two-tailed t-tests. Data in both panels represent the mean ± SEM from three independent experiments.</p

Schematic map of the six CNS tau isoforms.

<p>Exons 2 (E2), 3 (E3) and 10 (E10) are alternatively spliced to generate all six possible combinations. Arrowheads denote the position of the G55R mutation, present in four of the six isoforms. R1, R2, R3 and R4 denote the four imperfect repeats in the MT binding region.</p

A. The family tree of the affected family shows the pattern of inheritance.

<p>The proband is the black oval on the left side of the figure (II:1), marked with an arrow. Tau haplotypes of sequenced individuals are also noted. “aoo” corresponds to age of onset; “aod” corresponds to age of death; black filling indicates persons possessing the G55R mutation; gray filling corresponds to diagnosed dementia of unknown origin (presumed to be G55R but inadequate medical records exist). Proband's son III:1 (from first marriage) is 36 years old and a carrier of G55R. Proband's second son III:2 (from second marriage) is 31 and also a G55R carrier. The other two sons (III:3 and III:4; from the second marriage) are not G55R carriers and are 29 and 28 years old. <b>B. The tau sequence in the region of the G55R mutation is extremely highly conserved across species lines.</b> The glycine at position 55 is completely conserved in seven species ranging from humans to lizards. Color coding emphasizes conserved nature of acidic (red), basic (blue), hydrophilic/polar (orange), hydrophobic (green) and proline (peach) positions.</p