Structure Analysis of Two Toxoplasma gondii and Neospora caninum Satellite DNA Families and Evolution of Their Common Monomeric Sequence

CLEMENTE, M.; DE MIGUEL, N.; LIA, V. V.; MATRAJ, M.; ANGEL, S.O.

JOURNAL OF MOLECULAR EVOLUTION

Springer-Verlag

Lugar: New York; Año: 2004 vol. 58 p. 557 - 567

0022-2844

A family of repetitive DNA elements of approximately 350-bp -TGR or ABGTg repeats-  that are members of Toxoplasma gondii satellite DNA was further analyzed. Sequence analysis identified at least three distinct repeat types within this family that were called types A, B or C. Besides, B repeats can be divided in the subtypes B1 and B2. Searching for internal repetitions within this family permitted the identification of conserved regions and designing PCR primers that amplify almost all these repetitive elements. These primers amplified the expected 350-bp repeats and in addition they amplified a novel 680-bp repetitive element related to this family. Two different tandemly repeated high order structures corresponding to this satellite DNA family were found by searching the Toxoplasma genome database with these sequences and further confirmed  by sequence analysis: 1) an arrangement of  AB1CB2 350-bp repeats and  2) an arrangement of two different 350-bp-like repeats, resulting in a 680 bp monomer. Sequence comparison and phylogenetic analysis indicated that the current coexistence of both high order structures could have originated from the same ancestral 350-bp repeat. In addition, PCR amplification, sequence analysis and Southern blot showed that similar high order structures were also found in Neospora caninum, an organism closely related to T. gondii. Finally, the Toxoplasma genome database permitted the assembly of a contig harboring  Sat350 elements at one end and a long non-repetitive DNA sequence flanking this satellite DNA. The region bordering the Sat350 repeats contains two different expressed sequence related regions and interstitial telomeric sequences.